Modifying the Dynaco SCA-35

July 26, 2004

Welcome to my mod page for the SCA-35, especially all of you AudioXpress readers. In the August 2004 issue, the author of an article on modding the SCA-35, Mr. James Lin, states that little information is available about modification of the SCA-35. Hmm, that's wierd. This website has been online for over 8 years, and of them, this page has been here for 7 of them. Google much, Jimmy? Give a guy a little credit, will ya? Oh, and be a tissue and organ donor while you're at it, OK? Sheesh.

Anyway, about the picture above, NEVER stack them like this--I only did it for the photograph. (The amp gets way too hot to have the tuner sit on top of it.) Anyway, the SCA-35 is a roughly 13 watt-per-channel integrated push-pull 6BQ5 stereo amplifier, remarkable by most accounts for both its high-quality output transformers (very good) and low purchase cost (not always so good). Also remarkable is its PC-board construction (not too good) and simplified design (not too bad). It's an Ultra-Linear design, in that it uses screen taps on the primary of the output transformers, and it employs the 7199 dual pentode/triode as a driver tube (getting expensive--use RCA NOS). OK, that being said, how does it sound stock? Well, not bad, but not good. A little weak, hazy, light in the low end, hot-running, and somewhat fatiguing. How can it sound? With a few changes, clean with a lot of drive, and an easy fatigue-free sweetness.

Of course, a schematic is always helpful.  Fortunately, there is a fellow ham radio operator that has posted the amp and power supply schematics for the SCA-35 up on his website, which you can obtain by clicking here. If these ever become unavailable, email me and I will scan my own copy and post it here. For a full manual, I bought a binder full of Dynaco amp schematics that Sound Valves sells (and occasionally auctions off at eBay , which is where I grabbed them). They have two different collections, one for Preamps and Tuners and one for Amps, for $49 each.  I got both of them, and I'm glad I did.

May 30, 2000

Changes since the last revision (May25, 2000)

I now think that the 470-ohm 7199 pentode section cathode resistor is probably not the way to go. I fear that it is biasing the section on too hard, since almost all of the circuits published for the 7199 (by RCA and others) have a 820-ohm cathode resistor in that position. So, I decided to compromise a bit, and at the same time try an experiment on the positive feedback part of the circuit.

The pentode section cathode resistor is now 680 ohms (up from the stock 560 ohms).

And the stock 120K resistor that runs from the screen of the pentode to the cathode of the triode is now 150K, lessening the effect of the positive feedback. The one circuit in my RCA Receiving Tube Manual that shows the 7199 in a positive feedback mode driving a pair of 7868's (showing that this is not an Dynaco innovation) has a 180K resistor in this position, with an 820-ohm cathode resistor in the pentode section. So I went part of the way there, anyway. Little steps, I say.

While I was in there, I noticed that the 270K, 1-watt plate load resistor for the 7199 pentode was off from channel-to-channel--one was something like 284 ohms and the other was 271 ohms), so I put in a new pair of matched 2-watt Xicons.

After all of this, just to mess around, I drove each channel to a full 40V RMS (across a Dynaco A-25) with a 1 kHz sine wave, which equates to a bit over 14 watts, one channel driven at a time. Not bad. Sounds good, too. More to come, I'm sure.

May 25, 2000

Changes since the last revision (May 5, 2000)

Well, constant auditioning of the SCA-35 on the Electro-Voice Marquis, with their SP-12s, T-25A midrange horns and T-35 VHF horns (a 16 ohm speaker) and doing side-by-side comparisons with my HF-81 has led me to believe that the changes to the feedback circuit that sounded so good on the Dynaco A-25's (at considerably lower efficiency) were not suitable for the EV's. So back into the shop it went, where I spent some time researching the 7199 driver circuit. While I stopped short of redesigning it to take out the positive feedback Dynaco used to eliminate a dedicated linestage in the amp, I did do two things that affect the driver stage somewhat:

1. I went back to the straight 82K carbon compound feedback resistors, thus decreasing the feedback I had installed to compensate for the reduced passive loss of the bypassed tone controls.  It's now back to stock for the time being.

2. I measured the plate voltage of the 7199 pentode and found that it was way higher than the 55vdc the manual wants to see.  In fact, one side was 84vdc and the other was 77vdc.  Swapping the 7199's side-to-side made them a little closer to each other, but they were still high.  So I replaced the stock 560 ohm (they actually measured out at about 574 ohms) cathode resistors with a 470 ohm carbon films (that actually measured out at 462 ohms).  Now with another side-to-side swap, both tubes measure 71vdc on the plates.  Not 55vdc, but not 84vdc, either. Cathode resistor changed to 680 ohms--see above.

What of this?  Well, I'm listening to it right now, and it has taken about 20 minutes to settle down, but it seems cleaner.  Amazingly, even the tone-control-bypass mode sounds better--less edge and with more headroom.  With the tone controls in, the amp is easier to control and smooth, with a sweet top end that's there but not overbearing. Hey, it's a compromise design, after all.

I think it might be a good idea--as a last attempt to tame the positive feedback design before completely trashing it--to drop something like WIMA MKS-10 1.0mfd@400vdc caps in for the 1.0 mfd screen bypass cap. The 120K resistor from the screen to the cathode of the triode section from where it takes it's screen voltage makes this a positive feedback implementation, for as the signal across the triode section cathode resistor increases, the screen voltage of the pentode stage driver is also increased, thus increasing that stage's gain, ergo positive feedback. If I'm reading this wrong, let me know.

Otherwise, optimally it would probably behoove the serious knucklehead to fashion aluminum drop-in amp plates and redesign the driver altogether, but I'm not there yet.

May 5, 2000

Changes since the last revision (April 28, 2000)

Faster updates happening now--I got the last parts shipment today, so I replaced the last cathode biasing circuit I had in there, which was (for each channel) 180 ohms at 5 watts bypassed with a 100mfd@35vdc Radio Shack electrolytic cap.  I replaced all of that with (on each channel) 200 ohms at 5 watts bypassed with a 250mfd@25vdc Sprague Atom electrolytic cap.  Actually, the resistors came in at 197.2 ohms each, and I got two exact matched guys, as I bought 5 and picked the two closest--hey, they're cheap.  I had Yageo resistors in there--now they're Xicon, for what that's worth.  The amp runs cooler, which was one of my primary design goals, as the damned thing develops 368 volts on the plates (and 370 volts on the screens!), and at the present values one channel is seeing about 13.6vdc across its cathode resistor, and the other channel is seeing 14.0vdc.  This works out to almost exactly 35mA idling cathode current per tube, which, taking into account the probably 10mA idling screen current, leaves the output tubes at least a couple of watts (maybe) within their plate dissipation rating of 12 watts (they're regular Sovteks--I should get some Teslas for it, but these things refuse to die).

Result?  Very fat bass, slightly smoother mids, and I hope more consistent performance over time, as the amp should stay cooler.  (I should have measured the case temperature before and after--now I can do that, as the Protec DVM I recently got has a temperature measurement capability--nuts!)  We'll see how it sounds after the Spragues loosen up a little bit.

April 28, 2000

Changes since the last revision (April 10, 1999)

Whoa, an even longer silence--over a year!  Lots of email from enthusiastic owners, so I figured it was time to re-evaluate the SCA-35, in light of the experience I've had since I stopped working on it.  In that time, it was ensconced in my bedroom with the FM-3 tuner, driving a pair of mint KLH Model Four speakers, which present a very compatible 16 ohm impedance.  I've been very pleased with it, but I thought I'd audition it on the Electro-Voice Marquis speakers down here in the computer room, and besides, I just finished rebuilding an HK TA-3000X AM/FM Stereo receiver that had a walnut cabinet and took up less dresser space in the bedroom, so up it went and down came the SCA-35.  (The TA-3000X is not a bad receiver with Sovtek's new Electro-Harmonix EH6V6GT's, by the way.)

What I heard was a little stridency on the EV horns that was not noticeable on the KLH's or Dynaco A-25's I had originally voiced it on.

So as an initial foray, I changed out the 1N4007 rectifier diodes and went half-assed (which is my wont), using soft-recovery FR-107 diodes from AES ($.25 each).  Both are still individually bypassed with the same .01mfd@500vdc ceramic caps from Radio Shack as were the 1N4007's.  I also pulled out the .47mfd@630vdc Xicon (I think it was) metallized poly cap I had originally placed in parallel with the first filter cap section to ground.  Never liked that approach, despite its popularity among the boutique set--just adds a midrangey quality to the sound that drives me nuts.

So, while I await better cathode bypass caps for the EL-84's, this small mod has cleaned up some of the stridency I heard before the change.  Whether it was the diodes or the poly cap, who knows?  What I do know is that the two 100mfd@35vdc Radio Shack electrolytic cathode bypass caps that are in there now are coming out as soon as the 250mfd@25vdc Sprague Atoms get here from AES.

I guess I could go crazy someday and try HEXFREDs.  They are cheaper than GZ-34's, after all.  (I know they don't use a GZ-34 in this amp--doh.)

Oh, on hum reduction--right now I am enjoying a pretty quiet SCA-35, using flat-plate Telefunkens in the phono stage, RCA 7199's, and (I think they're) Sovtek EL-84's in the outputs.  The hum-balance pots actually null out the hum (most of it, anyway).  What you should try, aside from splitting up the cathode bias circuits as described below, is moving the output tubes around in their different sockets (as well as the phono stage tubes, of course), until you get decent nullability.  It's all inter-related, but I'd locate the 7199's so that the in-circuit as-measured plate voltage of each channel's pentode section is as close to balanced, channel to channel, as possible.  It should be approximately 90vdc, if I recall correctly.

April 10, 1999

Changes since the last revision (November 13, 1998):

Whoa--been a while.  I have to say thanks to all that have emailed me with their personal SCA-35 experiences, and in some cases even some thanks for what I always thought the Internet was supposed to be--a site for sharing of information.  In any case, some updates and/or changes (I think I may have even passed through some changes that never made it up to the page, here).

I pulled out the choke I added to the power supply described below.  Did this while pursuing the cause of excess hum in the phono stage, which I originally thought was due to the placement of the choke.  WRONG.  It was bad can caps, pure and simple.  I am as guilty as any of hoping that old can caps still work fine, but alas in this case, they were not.  It should not have surprised me, as this unit was apparently stored in an attic and had the dirtiest, blackest aluminum chassis I've ever seen--"good condition" the guy said up on eBay.  Right, like his Mom was in Good Condition after she had him/it.  But I digress...

I replaced the can caps with two LCR 500vdc electrolytics--a 40/20/20/20 and a 50/50. I also used a single 47mfd@450vdc axial electrolytic (AES-sourced), and arranged it all with the stock dropping resistors so that it looks close to the stock supply design. NOTE: the first section has a 40mfd and a 20mfd section of one LCR in parallel, and the second section has another 20mfd section of the same LCR plus the 47mfd axial in parallel, for a total of 67mfd that feeds the output stage. The rest of it should be self-explanatory. It's all wired like this:

Why did I do it like this?  Well, contrary to popular belief, the output tubes are connected to the SECOND section of the filter capacitor bank, not the first, so I opted to lump more capacitance on the point from which the primaries of the OPT's are fed.  Besides, I don't like the THUMP you get when you hit a big (uncharged) cap with immediate DC like you get out of a pair of silicon diodes.

As my unit was factory-wired, I had to drill out those steel rivets with a high-speed drill and pointed bit to get the bakelite capacitor mounting rings out.  Ugh, lots of work there.  But the good thing is that the LCR's with their above-chassis mounting rings DROP RIGHT IN!  Seriously excellent looking, too.  The trick is to bus-wire the negative terminals of both caps to a couple of lockwasher/solder lugs located on the mounting nuts--one on each cap, at opposing ends closest to the original grounding locations--and use them as ground ties for all the grounds that terminate in the filter cap area.  That's a lot, so use good big ground lugs.  Use a little excess lead length on the ground bus, as I had to keep turning the caps around in their mounting rings until I could get all the leads and resistor lead lengths to fit.  It's hard to plan 100% going in before you see where everything is going to fall.

With this refresh, the hum null balance pots actually work (!) in the phono position, and there is no more motorboating in the tape head position (or was that the HF-81?).  The amp sounds noticeably "faster", if that's a valid assessment, and everything's firmer and comes up from a darker, more quiet background.  Transients are fresh and realistic, and all is well.

Rebuild the power supply:

(See above update).

Add capacitance to the filter bank--if the existing can-type electrolytic cap is still good (mine seemed to be), then add a 47 mfd/450vdc axial electrolytic cap across the first section, a 33 mfd/450vdc across the second section, and another 47 mfd/450vdc across the last (fifth) section.  Note--this is haphazard at best.  If the can caps are replaced, a lot of this will be unnecessary--see above.

Change the original rectifier diodes to 1N4007's (or IXYS/General Semiconductor/International Rectifier Fast Soft Recovery Diodes), and bypass each of them with .01 mfd/500vdc ceramic caps (I used Radio Shack).

Replace the line cord with a 3-wire, 16-gauge line cord (or larger--again, I used Radio Shack), with .01@2KV (line-rated) caps from each side to chassis ground. You can use Panasonic X-Y Series (best) or Radio Shack ceramic caps (alright but not great).  This is a must-do, in my opinion.  The IEC says green is chassis ground, so attach that to the chassis (e.g., transformer mounting bolt if not insulated).  White is neutral, and goes to the unswitched side of the power transformer primary winding.  Black is HOT, so this goes to the AC power (on/off) switch.  Connect a .01@2KV from black to green and another from white to green at the point of entry of the line cord, and you're done.  Not more shocks, no more hum, no more code violations.

Add a 470 mfd/35vdc electrolytic bypass cap to the cathodes of the output tubes across the existing 95-ohm 5W WW resistor and the 100 mfd/25vdc part of the can-type electrlytic cap (again, if it's still good).  I split the output tube cathodes into separately biased pairs, using 180 ohm 5 watt wire-wound resistors each bypassed by a 100mfd@35vdc electrolytic cap.  I put it all on a 5-tab terminal strip (another Radio Shack acquisition) that I mounted just above the diode rectifier strip and over towards the center a bit.  Space was a slight issue, and although some use hefty bypass caps here--I use either 220mfd or 470mfd in other amps--the 100mfd caps fit and sound just fine.

Finally, add a .47 or 1.0 mfd/400vdc film cap (I used a Panasonic EF Series) from the output of the rectifiers to chassis ground (optional).

After some prodding from a friend (Dave Markman), I decided to play around with a choke in the power supply. I ripped a decent-sized choke out of a homebrewed 20-wpc stereo amp that looked to be the right size (no markings, natch), and substituted it for the first dropping resistor in the power supply, the one between the first and second capacitor sections. The choke measured (I think) 48 ohms resistance out of circuit, so I figured it would be a decent replacement for the 50 ohm, 5-watt resistor that came out.  The B+ on the output stage ended up rising, however, from 374 vdc to 381 vdc, which I hadn't expected. The EL-84's are still within their plate dissipation ratings, although they do run hot (which they like). The best thing is, though, that the bass tightened up perceptibly, and the sound is crystal clear, with no hint of graininess or ripple-induced distortion. Note--this is history.  See above.

The challenge in all of this is to locate the choke in a position that causes the least amount of hum in the phono stage. I finally settled on a location roughly .75" from centerline of the two can caps towards the power transformer, and an inch behind the pc board edge(s). This results in the choke's coil pack slightly overhanging the corner of the nearest output board. No matter--I had some hum in the phono stage anyway--it's no worse now.  I have to get to the bottom of that eventually, but it isn't bad. All in all, the choke is a valuable mod. The SCA-35 (and FM-3) have now graduated to the master bedroom, where they happily drive a clean pair of 16-ohm KLH Model Fours. Excellent. Ditto.

Replace All of the Coupling Caps:

I used a combination of 716P Orange Drops, Panasonic EF Series film caps, and ECI polyester film caps (available from AES), depending on how I felt, how much room there was, and so on. The original caps are these little blue mouse droppings that nobody has ever seen used in anything else, and which most people consider to be horrible. Actually, they don't sound all that bad considering, but as with any 30-year old amps, you can usually only improve them by putting in newer technology replacement caps. I didn't get too fancy here, as anything you put in there will be an improvement. As a guide, I used the following:

C6 --.1 mfd/250vdc Panasonic EF Series film cap (2 on phono preamp board)

C7 --.022 mfd/400vdc ECI polyester film cap (2 on phono preamp board)

C8 -- .1 mfd/400vdc ECI polyester film cap (2 on phono preamp board)

C17 -- .1 mfd/250vdc Panasonic EF Series film cap (1 on each channel amp board)

C18 -- 1.0 mfd/400vdc ECI polyester film cap (1 on each channel amp board)

C19, C20 --.1 mfd/400vdc 716P Orange Drop (2 on each channel amp board)

I used all original values. For now, check the schematic to identify each cap. I'll put up a description when I get a chance to check it. Note that my schematic had an error--C18 is shown as a .1 mfd, when it's in reality a 1.0 mfd.

Check and Replace the Critical Resistors:

The important ones here are mostly grid resistors and phase inverter plate and cathode resistors. Carbon composition resistors go high with age (usually), so check first the 470K grid resistors on the 6BQ5's, and to be safe, since they affect the balance of the push-pull output stage, replace them all with a measured and matched set of four--I used Radio Shack 1/2-watt 5% carbon films. Again, nothing fancy. Then check the 7199 pentode and triode grid resistors, and the 7199 triode plate and cathode resistors--make sure they are as specified, and replace as necessary. Mine were OK, as I remember, so the only ones I believe I ended up replacing were the 470K's I mentioned.

Remove the "Filter" Function:

This guy is useless, and we need the switch for the next section, so remove the four .033 caps (the little blue things), and all of the wiring, then rewire the wires from the Volume control back to the Stereo/Mono slide switch where the other two leads from the Filter switch used to connect, thereby effectively removing the switch from the circuit. Save the two other (longer) wires from the Filter switch--we'll use them below.

Install a Tone Control Bypass Function:

This is very cool--and now, even more so. Previously, as described in the first section below, I basically used half of the former Filter switch as an SPST switch to short out the tone control circuit. As Jason Petrisko pointed out to me in an email, he noticed (as did I when I tested it), a slight treble roll-off when the Treble control was turned down, even with the tone controls shorted out. So to the bench I went. I ended up having to accept a compromise--it turns out that even when using the full DPDT function of the switch to disconnect either the input or the output of the actual tone control circuit, there remains either slight treble roll-off, or slight bass roll-on--your choice. I chose the latter. In actuality, however, as the original circuit was allegedly designed for minimum phase shift when adjusted to the "center" position (as described in the manual--it varies for each control, Bass and Treble), they should present no sonic problems when bypassed, even if they are only merely shorted out. But for the sake of completeness, I will present my original simple mod and a mod to the mod, as follows.

The simple mod: With the two long wires removed from the Filter switch above, connect the middle two sections (the wipers--one per channel) of the former Filter and soon-to-be Tone Control Bypass switch to the wipers on the Volume control (not the loudness control taps). Then wire the right tabs of the switch--as seen from below with the front panel away from you--to the "top" of each channel's Balance control section. The "top" of the Balance control is at one end of the Balance control for one channel--the other end, or electrical "bottom" is connected to ground--and at the other end for the other channel (each channel is wired opposite from the other in other words), so be careful. If you use the left-over Red and Green wire, you'll be able to follow and wire it without too much trouble. The big benefit of this change is a huge increase in available gain--probably around 20 dB or more, and the amp sounds less constricted to boot. The nice thing is that with the flick of a switch (so to speak--slide switches don't really flick), you can return to normal operation (but you won't--trust me). As described above, the circuit is now stock with tone controls when the switch is in the "Filter" position, and modified with the tone controls bypassed with it in the "Off" position.

The mod to the mod: In this approach, the tops of the Balance control are connected to the wipers of the Filter switch, and the wipers of the Volume control are connected to the "Filter Off" side of the DPDT Filter switch. Then the inputs to the tone control circuit, normally connected to the taps on the tone controls, are connected to the other end of the switch (the "Filter On" position). This requires relocating them from their original connections to the Balance control(s), using a couple of pieces of wire. In this configuration, when the Filter switch is set to Off, denoting bypass, the connection from the wipers of the tone controls is completely disconnected from the circuit, instead of being in parallel with the bypassing function of the original SPSTshorting design. In this modification, a very slight bass roll-on is noticeable if the Bass control is turned full on (not an entirely disagreeable feature). However, this eliminates any loading on the treble side, which I think is preferable to the original design described above--comments are invited.

Modify the Negative Feedback:

This particular mod has had me guessing a bit, and has changed a couple of times as a result. Before I put in the Tone Control Bypass function, I took out the 12 pf screen feedback caps and replaced the 82K global feedback resistors with 100K's paralleled with 39 pf. I felt that this reduction in feedback opened up the amp a lot. After bypassing the tone controls, however, I found I had to return to the stock circuit. But now, after even more time on it, I decided that I could do better, so I struck a median value based mostly on stock-on-hand, but with a little analysis--if you can call it that--of what the ST-35 and the EICO HF-81 use. Suffice to say I ended up keeping the 12 pf screen feedback caps (I'll go to silver mica some day), but replaced the 82K global feedback resistors with 47K paralleled with a 39 pf silver mica. Although this amounts to some 8 dB or so additional feedback over stock, it sounds nearly perfect. No more sizzling highs and weak bass. In fact I think I may be finally DONE (well, Phase One, anyway). In any case, feedback is an area where I need a little more theoretical background. I have the test equipment to pump a square wave into the amp and look at the output on a scope across a non-inductive load, but so far I've just gone by my ears. That, a little intuition, and a lot of perseverance--works for me. My excuse is that sometimes knowing too well how something works can take too much of the mystery out of it, and we don't want that. Well, maybe we want a little bit of it. Nah.  This is another must-do, as long as the tone controls have been bypassed.  Nothing else I've done has improved the SCA-35 as much as this change.

Replace the Tubes:

I've dicked around with various tubes in my SCA-35, and am always trying something different, it seems. The choice of preamp tubes has a big influence on the ability of the amp to be hum-balanced. New Sovtek 12AX7WXT+'s seem decent in this regard, as are older RCA's, while I've frankly had less luck with Mullards and Telefunkens, although they sound better, in that order (in my opinion, that is). Actually, if I could, I would only use Mullards for things like tuner output stages, imtegrated amp line driver stages, even rectifiers, and so on. To me, nothing else comes close to Mullards, from either a sonic perspective or in the case of rectifiers, performance perspective. Actually, for 12AX7's, Brimar seems close. Anyway, as the 12AX7's are only used when using the phono input, you can select for low hum and noise if you are not running a turntable, and for sound if you are. Also try swapping tubes from channel to channel to further reduce hum--the same goes for the 7199's. The manual mentions that the adjustment point for the least amount of hum is different for the phono stage than it is for the higher level inputs, but from my experience, if you adjust it for the least amount of hum in Phono, it's inaudible for Radio, Spare, etc.

Speaking of the 7199's, I strongly recommend getting NOS RCA's, for less hum and noise. I got mine from Ned Carlson at Triode Electronics (www.triodeel.com). And for the output tubes, I've tried everything from the original RCA's, to new Tesla's and Sovtek's, and even Yugoslavian-sourced GE's from the early 80's, but am now running a pretty closely matched quad of Soviet mil-production EL-84M's I pulled from my Audio Note OTO SE Phono, dated 1990. They seem to run cooler, and sound fine. I also liked the cheap Sovtek 6BQ5's, which you can't beat for the price. But what is very important is that they are matched as a quad, as they all share a common cathode bias resistor. So do yourself a favor and buy a nice new quad--they're cheap enough. I'm using the cheap and musical Sovtek 6BQ5/El-84's and loving them, mostly because they're cheap.  When I tried the EL-84M's, I rather liked them better, but they already have a home in my Audio Note OTO SE Phono, where they came from.

Probably the next mod I will be trying is implementing the more common split channel cathode bias arrangement with two separate resistors and their respective bypass capacitors--one combination per channel pair of output tubes (duh). The only company I've ever seen do it the way Dynaco does with the SCA-35 (and ST-35) is Heath, with their AA-151 (also a push-pull 6BQ5 amp). By the way, the SCA-35 manual mentions that the single cathode bias resistor in the output stage arrangement yields a performance enhancement. I would like to have this explained to me, if anyone can. The common assumption is that it was done for cost reduction purposes.  I received an email explaining this design choice, but regardless, went to split bias resistors, as described above.

Sit Back and Let 'er Rip:

When you think you're done, plug everything in, balance the hum with the two pots on the back panel, and try some program material. Actually, it's smart to do this at each stage of mods, so you don't have a problem and lose track of what you just did, which probably caused it. This is a Work in Progress, by and large, but without getting into any major overhauls of the design of the amp, this is probably where you can stop. What you will have when you are done (especially with the tone controls switched out), is essentially a power amp with a passive preamp on the front end, like a Jolida, for example. Unlike some designs with a little more money behind them, there really is no line amplifier in the SCA-35. That is one reason the tone controls have such a dramatic effect on the sound. And with the built-in phono preamp (albeit one that is a little on the simple side), you have a nice low-powered vacuum tube integrated amp with a phono front end. Try to find that out there for less than a grand.

Hope you like it. I do. Makes a great little system with a tweaked FM-3, a portable CD player (really!), and a pair of Dynaco A-25 speakers. Have fun and let me know how you make out.

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