St-35
Ok Im, not a tube god and do not profess to have great knowledge in the field of tube amplifiers. That said, I have just come into a fairly beat Dynaco st-35. There are no tubes in it and the circuit boards look to have been hot for a long time but transformers look OK.
My question is this: Is it worth restoring this thing back to it's original circuitry or has time left this design so far behind it's better to just scrap it for parts (transformers) and build something with a more modern topology. On the one hand I could end up with nice classic amp. On the other hand if it does not sound that great why bother. There seem to be allot of designs around using dynaco transformers with more up to date designs. Is there any sense of agreement on what to do with an old st-35
Thanks
Ok Im, not a tube god and do not profess to have great knowledge in the field of tube amplifiers. That said, I have just come into a fairly beat Dynaco st-35. There are no tubes in it and the circuit boards look to have been hot for a long time but transformers look OK.
My question is this: Is it worth restoring this thing back to it's original circuitry or has time left this design so far behind it's better to just scrap it for parts (transformers) and build something with a more modern topology. On the one hand I could end up with nice classic amp. On the other hand if it does not sound that great why bother. There seem to be allot of designs around using dynaco transformers with more up to date designs. Is there any sense of agreement on what to do with an old st-35
Thanks
greetings, I think either approach is valid but to cover yourself you could build a new chassis and try a different topology using the tfmrs (which were always considered very good) so you can always pop them back in the st35. I think you can do much better sound wise t han the original circuits using a seperate phase slpitter rather than that triode/ pentode 7199 tube which while it worked quite well was proobably a cost saving measure in the first place. There is plenty of info on the net and I remeber a site where a guy had a step by step process of doing what you are thinking except he got his tfmrs from a sca35 but same diff. Especially that it a is a beat up one in the first place I think, to coin a well used phrase" out of the ashes the pheonix rises"
cheers and good luck cheers fergs
cheers and good luck cheers fergs
I agree with keeping the transformers and tossing the rest. Check out www.diytube.com - they sell a pcb for a st-35 type circuit. It's a good project, especially if you already have the iron for it.
My take - restore it... this is one of the the rarest Dynaco amps, and will be worth much more than the cost of restoration. Some think it's the best sounding one too.
If I recall correctly, this used 12DW7s/7247s, not 7199s, and they aren't THAT expensive, with new production available. I think there are new PCBs available in the original color...
If I recall correctly, this used 12DW7s/7247s, not 7199s, and they aren't THAT expensive, with new production available. I think there are new PCBs available in the original color...
You owe it to yourself to at least get it operating condition, listen to it, and decide for yourself what you will do. (and I'll bet you'll be quite surprised!) It's not a powerhouse, however, and requires speakers of , at least moderate efficiency. The 17.5 Watts/ch rating is a little bit of a stretch! The output transformers are considered among the best ever built and are in demand! The power transformer is stressed fairly hard and has been know to fail from time to time, although it's not a problem, as improved replacements are easily available. Give it a try!
st--35
Thanks to everyone who replied. I suppose I should have guessed before hand that I woulf get near an even split on the rebuild verse gut question. It looks like a new populated set of st-35 boards ould set me back about $100 and and the diytube boards would be about $ 130. But I loose another $35 replacing the 3 section electrolytic with a similar unit (I just guessng its bad but its hard not to believe it shouldn't be replaced anyway).
The new pc board then requires a new chasis for about $80 but the rebuilt original will still be sitting on a chasis which clearly didn't have enough ventilation. Overall it still seems about equal what the best thing to do is.................
Any thoughts on which 6BQ5's represent a decent deal? Seems silly to put premium tubes in a low end amplifier.
PS fist job for this thing if I ever get it working will be to take over driving my old Stax ESL headphones
Thanks to everyone who replied. I suppose I should have guessed before hand that I woulf get near an even split on the rebuild verse gut question. It looks like a new populated set of st-35 boards ould set me back about $100 and and the diytube boards would be about $ 130. But I loose another $35 replacing the 3 section electrolytic with a similar unit (I just guessng its bad but its hard not to believe it shouldn't be replaced anyway).
The new pc board then requires a new chasis for about $80 but the rebuilt original will still be sitting on a chasis which clearly didn't have enough ventilation. Overall it still seems about equal what the best thing to do is.................
Any thoughts on which 6BQ5's represent a decent deal? Seems silly to put premium tubes in a low end amplifier.
PS fist job for this thing if I ever get it working will be to take over driving my old Stax ESL headphones
Re: st--35
By all means gut it. Personally i wouldn't bother with the chassis either. Leading contenders are El Cheapo, Red Light District & Baby Huey (or mix & match)
For new, JJs get pretty good mention (i've not tried them). You can also get good prices from some of the Eastern European vendors on the Russian equivalent of EL84Ms (6p15p?).
And then you might just be able to tap someone for junkers during the test phases,
dave
By all means gut it. Personally i wouldn't bother with the chassis either. Leading contenders are El Cheapo, Red Light District & Baby Huey (or mix & match)
sds2000 said:
For new, JJs get pretty good mention (i've not tried them). You can also get good prices from some of the Eastern European vendors on the Russian equivalent of EL84Ms (6p15p?).
And then you might just be able to tap someone for junkers during the test phases,
dave
a few random thoughts on the ST35 (in no particular order)
"Low power"?
While moderate to low sensitivity designs continue to predominate mainstream commercial loudspeakers, there are more than enough very simple DIY designs for which 17.5 watts or thereabouts is more than enough for most domestic listening situations. Consult the Fullrange loudspeaker section of these forums for any number of designs.
"Low end amp"?
Dynaco products were about putting the most musical performance in the hands of as many DIYers for as low a price as possible. Of course once the beancounters got involved, this meant cutting dollars and cents where ever possible on parts, resulting in some compromises in performance or lifespan. No doubt Dave Hafler and his associates couldn't predict the collectability these products would enjoy 40+ years later.
With selective replacement of even only the most defective or aged components, the ST35 is not a low-end amp.
"Restore"?
However, having said that, the best thing about these amps is the quality of the output transformers. Several of the newer DIY circuit designs mentioned above would sonically outperform the original ST35 design, and likely for far less money than would be entailed in a complete restoration.
For example, I've built 2 examples of a variation of the El Cheapo with recycle Scott iron, and much prefer them to my (slightly modified) Jolida 302.
Depending on how far gone the chassis is in terms of corrossion or other damage, it might be worth considering the offerings of Triode Electronics: it could easily take more time and material to refurbish a beat-up chassis than the price of these new.
"Low power"?
While moderate to low sensitivity designs continue to predominate mainstream commercial loudspeakers, there are more than enough very simple DIY designs for which 17.5 watts or thereabouts is more than enough for most domestic listening situations. Consult the Fullrange loudspeaker section of these forums for any number of designs.
"Low end amp"?
Dynaco products were about putting the most musical performance in the hands of as many DIYers for as low a price as possible. Of course once the beancounters got involved, this meant cutting dollars and cents where ever possible on parts, resulting in some compromises in performance or lifespan. No doubt Dave Hafler and his associates couldn't predict the collectability these products would enjoy 40+ years later.
With selective replacement of even only the most defective or aged components, the ST35 is not a low-end amp.
"Restore"?
However, having said that, the best thing about these amps is the quality of the output transformers. Several of the newer DIY circuit designs mentioned above would sonically outperform the original ST35 design, and likely for far less money than would be entailed in a complete restoration.
For example, I've built 2 examples of a variation of the El Cheapo with recycle Scott iron, and much prefer them to my (slightly modified) Jolida 302.
Depending on how far gone the chassis is in terms of corrossion or other damage, it might be worth considering the offerings of Triode Electronics: it could easily take more time and material to refurbish a beat-up chassis than the price of these new.
I also recommend cleaning the unit up and listening to it. Replace the quad cap and any other electrolytic caps in it (cathode bias bypass). I'd also replace all the old carbon comp resistors and awful coupling caps with good quality film caps and metal film resistors and give it a listen.
Then you have a baseline for comparing the original to any changes you make.
Hafler did a very good job balancing performance with cost cutting needs. It's a quite capable amplifier as it is. You can do a lot of changes and make it a lot more complex and not end up with a better product.
I have an SCA 35 that I've completely rebuilt and removed the balance and tone control sections (basically selector to noble pot to amp boards) and it is a great sounding little amplifier, much better sounding than many other more expensive peices out there. If you have sensitive speakers (I have the Quad ESL's for example), I'd take a ST-35 over a pair of MKIII's (or any modern tube gear at any price) any day.
I find that the ST-35 to be the nicest of the Dyna amp line but you may need a bit more power. the ST-70 is nearly as nice, and will drive pretty much anything, the MKIII's offer more power but don't really do much for me musically. I'd take a citation II WAY before a set of MKIII's.
Also, in my limited experience building amps, I find that the split load inverter works very well with small output tubes. It's great with the EL84 and similar power tubes. It will do OK with the EL34, and it completely marginal with bigger tubes like the KT88. The split load inverter is not ideal because the output impedance for each phase is different, but the easier the load, the less that matters. Ideally, you’d have a Heathkit/ Williamson type of driver stage if you had your heart set on a split load inverter. The first triode is voltage gain, which drives a split load inverter, then that feeds a set of low gain stages. The split load inverter drives the grids of the tubes that drive the output tubes.
Sheldon
Then you have a baseline for comparing the original to any changes you make.
Hafler did a very good job balancing performance with cost cutting needs. It's a quite capable amplifier as it is. You can do a lot of changes and make it a lot more complex and not end up with a better product.
I have an SCA 35 that I've completely rebuilt and removed the balance and tone control sections (basically selector to noble pot to amp boards) and it is a great sounding little amplifier, much better sounding than many other more expensive peices out there. If you have sensitive speakers (I have the Quad ESL's for example), I'd take a ST-35 over a pair of MKIII's (or any modern tube gear at any price) any day.
I find that the ST-35 to be the nicest of the Dyna amp line but you may need a bit more power. the ST-70 is nearly as nice, and will drive pretty much anything, the MKIII's offer more power but don't really do much for me musically. I'd take a citation II WAY before a set of MKIII's.
Also, in my limited experience building amps, I find that the split load inverter works very well with small output tubes. It's great with the EL84 and similar power tubes. It will do OK with the EL34, and it completely marginal with bigger tubes like the KT88. The split load inverter is not ideal because the output impedance for each phase is different, but the easier the load, the less that matters. Ideally, you’d have a Heathkit/ Williamson type of driver stage if you had your heart set on a split load inverter. The first triode is voltage gain, which drives a split load inverter, then that feeds a set of low gain stages. The split load inverter drives the grids of the tubes that drive the output tubes.
Sheldon
I certainly agree with Sheldon on the MKIII vs Citation II - my experience early on with both amplifiers - even when heavily modified the Citation II iron is so superior to the Dyna iron there is no contest.
More on topic. The ST-35 is a pretty decent sounding amplifier even stock, and the output transformers are good quality. (No match for an Acro 2020 though)
Like the Realistic amp I am restoring the ST-35 runs the 6BQ5 way beyond its ratings. I have found that the JJ really doesn't stand up well to this kind of abuse, although it is great sounding and really actually exceeds its maximum rating specs by a considerable margin. I think the EL84M is a safer bet or better still if you can score some 7189 these will handle the elevated plate voltage and dissipation.
IIRC the screen and plate dissipation in the ST-35 probably exceeds 14W per tube.
I have never figured out why people ran EL84/6BQ5 so far beyond their ratings, but apparently Mullard, Amperex, Toshiba, and some US brands can survive long periods of operation at 100V and 25% - 30% beyond their dissipation rating. Current production can't quite.
I have some NOS RCA that definitely cannot be run this way as well so it is no reflection on the quality of current JJ production.
OT: My recently acquired Realistic Stereodyne/40 (long story) runs them at 390V+ and 50mA per tube cathode bias. The original japanese tubes don't glow, some of the new JJ's do..
All caps and critical resistors have been replaced. Sadly this particular amp is pretty ugly, new ones were handsome in the eyes of a 4 - 16 yr old over 3 decades ago, a mint one might still be.. Sounds pretty good for a cheap amp.. Another sleeper Realistic Stereo 24 from a few years later.
More on topic. The ST-35 is a pretty decent sounding amplifier even stock, and the output transformers are good quality. (No match for an Acro 2020 though)
Like the Realistic amp I am restoring the ST-35 runs the 6BQ5 way beyond its ratings. I have found that the JJ really doesn't stand up well to this kind of abuse, although it is great sounding and really actually exceeds its maximum rating specs by a considerable margin. I think the EL84M is a safer bet or better still if you can score some 7189 these will handle the elevated plate voltage and dissipation.
IIRC the screen and plate dissipation in the ST-35 probably exceeds 14W per tube.
I have never figured out why people ran EL84/6BQ5 so far beyond their ratings, but apparently Mullard, Amperex, Toshiba, and some US brands can survive long periods of operation at 100V and 25% - 30% beyond their dissipation rating. Current production can't quite.
I have some NOS RCA that definitely cannot be run this way as well so it is no reflection on the quality of current JJ production.
OT: My recently acquired Realistic Stereodyne/40 (long story) runs them at 390V+ and 50mA per tube cathode bias. The original japanese tubes don't glow, some of the new JJ's do..
All caps and critical resistors have been replaced. Sadly this particular amp is pretty ugly, new ones were handsome in the eyes of a 4 - 16 yr old over 3 decades ago, a mint one might still be.. Sounds pretty good for a cheap amp.. Another sleeper Realistic Stereo 24 from a few years later.Yah, just to echo what Kevin, Sheldon and others said.
I refurbished a few and found them quite good. Only the funny 7247 (two dissimilar triodes) was blastedly expensive to import here, and I replaced with ECF80s with minor changes on the p.c. (Not 7199s in those.) I am not fond of hi-mu triodes as power amp input stages; prefer pentodes - but not to start that again. To each his own.
I do echo the overly high h.t. and plate dissipation of the EL84s. I also found it rather funny to save to the extent of using a common cathode (bias) resistor for all four EL84s. Really.
The few watts gained over usage within ratings make less than 2 dB difference, which is not worth the excercise. Otherwise to my mind a fine little amplifier in that class.
Regards
I refurbished a few and found them quite good. Only the funny 7247 (two dissimilar triodes) was blastedly expensive to import here, and I replaced with ECF80s with minor changes on the p.c. (Not 7199s in those.) I am not fond of hi-mu triodes as power amp input stages; prefer pentodes - but not to start that again. To each his own.
I do echo the overly high h.t. and plate dissipation of the EL84s. I also found it rather funny to save to the extent of using a common cathode (bias) resistor for all four EL84s. Really.
The few watts gained over usage within ratings make less than 2 dB difference, which is not worth the excercise. Otherwise to my mind a fine little amplifier in that class.
Regards
"El Cheapo" was mentioned by Dave D. (planet10). The "basic" schematic is here. If you have the time, "wade" thru the lengthy thread.
The ST35 trafo set allows for a tube rectified B+ variant of "El Cheapo". EC requires a "360" V. B+ rail. The heater current requirements (2.4 A.) of 4X 6V6 family "finals" and 2X 12AT7 splitter/drivers can be taken from 1 of the 2X 6.3 V/2.5 A. windings on the ST35 power trafo. The B- rail can be obtained, via a voltage multiplier, from the 2nd 6.3 VAC winding. My guess for the rectifier tube is a 5U4. A 5 VCT/3 A. filament trafo is needed by a 5U4. The Hammond 266M5 fills the req. CLC filtration is indicated. The Hammond 159S choke should do the job.
The ST35 trafo set allows for a tube rectified B+ variant of "El Cheapo". EC requires a "360" V. B+ rail. The heater current requirements (2.4 A.) of 4X 6V6 family "finals" and 2X 12AT7 splitter/drivers can be taken from 1 of the 2X 6.3 V/2.5 A. windings on the ST35 power trafo. The B- rail can be obtained, via a voltage multiplier, from the 2nd 6.3 VAC winding. My guess for the rectifier tube is a 5U4. A 5 VCT/3 A. filament trafo is needed by a 5U4. The Hammond 266M5 fills the req. CLC filtration is indicated. The Hammond 159S choke should do the job.
I have 3.5 (depending how you count, I guess) ST-35s, which I've been using for about 20 years, total. I experienced my first filter cap failure a couple months ago, so I think the quality of this item is pretty good. I do, however, use a Variac to control the line voltage, which runs over 125 volts most of the time!
I haven't gone through more than 3-4 output tubes during the same time period,also. Perhaps the controlled line voltage helps in that respect, also. My current Telefunkens test about the same now as when installed 10 years ago. I wish they were still available, although the set of JJ's that I just got appear to have almost identical internal construction.
On another note, would anyone like to venture a guess as why the concertina phase splitter is deliberately unbalanced, with differant value resistors in the cathode and plate circuits?? I 've never heard any sort of resonable (or otherwise) explanation for this. Perhaps the positive feedback link to the voltage amp. has some bearing on this?
I haven't gone through more than 3-4 output tubes during the same time period,also. Perhaps the controlled line voltage helps in that respect, also. My current Telefunkens test about the same now as when installed 10 years ago. I wish they were still available, although the set of JJ's that I just got appear to have almost identical internal construction.
On another note, would anyone like to venture a guess as why the concertina phase splitter is deliberately unbalanced, with differant value resistors in the cathode and plate circuits?? I 've never heard any sort of resonable (or otherwise) explanation for this. Perhaps the positive feedback link to the voltage amp. has some bearing on this?
On the SCA-35 board I designed, I got rid of the single cathode resistor for all four tubes and split that into a more sensible one resistor for each pair. I also raised the value a bit (more than doubling it) to lower the tube dissipation below 12 watts.
I was just listening to mine a few minutes ago while auditioning a pair of quads I just rebuilt. It's a nice little amp, no question about it. Not the absolute best, but man is it musical, just like the quads.
Sheldon
I was just listening to mine a few minutes ago while auditioning a pair of quads I just rebuilt. It's a nice little amp, no question about it. Not the absolute best, but man is it musical, just like the quads.
Sheldon
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