[FrankCooter]

I'm late to the party but I'll chime in anyway. Here's what I'd do:

1) Reverse engineer the circuit. Draw a schematic with all the voltages and currents labeled.

2) Gut it. No matter how bad your layout and soldering skills, it will be better than what you have now.

3) Replace the tube sockets with something of quality. Use some decent audio grade resistors. I like carbon types, such as Kiwame. When you replace the rectifier diodes, go for a safety factor of 5 or 6. Tube filaments have big inrush currents, particularly something like a 6bl7. The power transformer is definately a Hammond 272 type. By getting a rough voltage measurement of the output, and using the physical dimensions given on the Hammond web site, you shouldn't have too much trouble figuring out what you have. You might want to replace it with a 300 series. The 272 is noisy and runs hot. It's a minimalist design. Try the Russian PIO capacitors from Ebay for coupling positions. They are cheap and sound exellent. If that 100mf electrolytic is really simply in parallel with the 220 film cap, leave it out. If you need more filtering, add another RC section with a second film cap. Keep roughly the same operating points, but don't sweat a 5 or 10% difference. The tubes won't care, and I'm sure the designer didn't either

 

[FallenAngel]

Started drawing the schematic, the HV and filament supplies are drawn out, actual tube circuit coming soon. Some stuff looks a little unsafe (no bleeders, etc).



I just cut off and threw the filament supply in the trash, rebuilding to "almost same" but with decent diodes and and caps. I'm also going to be using both filament windings on the transformer - 6.3V/3A for output tubes, 5V/2A for driver tube.

Looks like that 100uF electrolytic is in fact parallel with the 220uF film cap. I'll keep it because there is a resistor across it - looks to be there for "easiness".

Really need to find a good output cap for this amp Suggestions? I'm kind of looking at the Jensen electrolytic caps.

Would also really love to know what people think of putting those 10uF/450V caps in parallel and series in the HV supply - is this really a good idea? I'm thinking of replacing them with 2x 20uF Panasonic TS-series.

 

[KZEE]

Quote:

Originally Posted by skyline889 /img/forum/go_quote.gif I think some people forget that not all Singlepower amplifiers were crap. The later ones yes, the earlier ones, no.

I don't know what is considered early, but 4 or 5 years ago I bought a new PPX3 from Singlepower, and the amp sounded so bad that I sent it back to Singlepower and traded up to an MPX3 (one of the hardwired ones). The MPX3 was an improvement over the PPX3, but not by much, so I sold it.
Now that it's coming to light just how poorly Singlepower products are designed and constructed, I now understand why my PPX and MPX amps sounded so bad.

 

[kevin gilmore]

Everything Frank Cooter says and then some. In spades!

first some schematics of other units i've worked on for an indication of the
glory of singlepower. The first one is closer to yours. Now in glorious scaleable
pdf's...

http://gilmore.chem.northwestern.edu...supraphils.pdf

and the truely frightening high voltage switchable version

http://gilmore.chem.northwestern.edu...ehoursupra.pdf

As far as output capacitors, this is what you really want
http://gilmore.chem.northwestern.edu/bigcap2.jpg
1000 volt 1000uf teflon film caps.

2 problems with this, you will never find any
(and i'm not giving any of mine away)
and even if you did, you would not get them inside the chassis.


The 220 uf Solens are one of the few film caps big enough for the job.
specs below.

220uf / 400v 0.002df PB 2.48 x 4.53 (63x115) $51 each

Quote:

Would also really love to know what people think of putting those 10uF/450V caps in parallel and series in the HV supply - is this really a good idea? I'm thinking of replacing them with 2x 20uF Panasonic TS-series.

series and parallel caps without bleeder resistors is a REAL BAD idea.

 

[nurxhunter]

""
Quote:
Originally Posted by skyline889 View Post
I think some people forget that not all Singlepower amplifiers were crap. The later ones yes, the earlier ones, no.

""I want to see internal pictures of these non-crap ones. ""

Removed pics. Can't seem to find link. Try and keep everyone happy.

 

[FallenAngel]

Please scale down your photos, or better yet, link to them.

Thanks Kevin and Frank.

I think I'll replace trashing the filament supply altogether, will replace with a single Amveco 7V/5A toroid - Digi-Key - TE62070-ND (Manufacturer - 62070)

Replacing those 4 10uF caps with a pair of 33uF Panasonic TS-HA/TS-HB

Should I be adding bleeder resistors across the HUGE caps?

 

[ServinginEcuador]

Wow, thanks for taking the time to document your journey with us FallenAngel. I'd like to see what, if anything, needs to be done to my incoming Supra. If I can improve the sound at all, and add some extra safety at the same time, I'm all for it.

 

[nikongod]

If you have not thought to yet (or found out as I did), please discharge the output caps before you work. They hold voltage on most OTL tube amps. The heater caps also hold HV.

Whats up with such a complicated heater supply? You can EASILY get away with something as simple as mikhail used with all but 0.1% of tubes, or even AC heaters in an amp like this if you are willing to write off 2-3% of tubes as hum-dumpsters. Whatever you decide to do, be sure to float or bias the heaters to accommodate the various cathode voltages about the amp. Vhk limits will eat your tubes like a hungry velociraptor if you ground the heaters to signal/chassis ground.

 

[FallenAngel]

Thanks for the heads up - I've been obsessively careful with this thing.

I'll keep the filament supply same, just add a different transformer - Triad 6VAC @ 8.34A Toroid and upgrade parts.

Still on the lookout for an output cap to replace those monsters. I think I found a candidate! BlackGate NH 220uF/160V at $32.50 from Percy!

 

[ServinginEcuador]

Quote:

Originally Posted by FrankCooter /img/forum/go_quote.gif You might want to replace it with a 300 series. The 272 is noisy and runs hot. It's a minimalist design.

Frank,

Is it worth it to upgrade to a 300 series transformer? My current "toaster" version of the Supra with 6BX7/6BL7 tubes has a Hammond 278X transformer, and for about $175 I can get a 378X from DigiKey, but am curious about how it will the sound of the amp. Running cooler would be nice as this thing runs pretty hot after running for a few hours, but the cost of the transformer and installation would have to be worthwhile sound wise, not just transformer operating temp-wise.

 

[digger945]

If you don't care and your not in a hurry you can score a 378 on ebay for less. Some are used but some lately are nib.

 

[FallenAngel]

Great idea about eBay! I just snagged a Hammond 372FX with 5A 6.3V secondaries for $85! I was about to pay $30 just for the filament transformer!

 

[FallenAngel]

Ok, so I think I'll be replacing those nasty looking cathode bypass caps as well - just gotta verify voltage - it's very low? Cap is 25V, but I'm planning to stick a 16V BlackGate STD in there as I think the voltages are actually closer to 7V, not 25V.

 

[FallenAngel]

Well, I think my SinglePower adventure is complete.

Transformer: Replaced with Hammond 372FX.

Filament supply:
4x FES16DT diodes
2x 4700uF/16V Nichicon HE
Output voltage is 6.54V, close enough for me.

High voltage PSU:
2x DSEP12 diodes
Nasty 4x 10uF caps replaced with single 47uF/450V Panasonic TS-HA

Cathode Bypass caps:
BlackGate STD

Output caps:
220uF/160V BlackGate NH-series bypassed by 0.22uF Auricap for that "classic" tube amp combo.

I also replaced those terrible RCAs with some decent CMC ones from VT4C (not in internals photo).

Overall, it sound nice, but honestly, at the price of the base amp, plus "upgrades" put in by designer, plus my parts cost, I was expecting better. I have no doubt it's good for an MPX3, but I'm not overly impressed. Oh well, live and learn.

Now to play with tubes. Right now I'm running Tung-Sol 6SN7GTB driver and 2x Tung-Sol 6BX7GT for outputs. I don't have much of a collection, time to buy some 6SN7s and play around a bit.

Photos:

 

[thathertz]

Great job. Glad you got it sorted!

Out of interest, which of your phones sound the best with your MPX3?