[shellylh]

Quote:

Originally Posted by seasterl /img/forum/go_quote.gif Sorry to be somewhat off-topic, but I haven't had time to read all of these posts yet. But I did read the very first post, and noticed the rat's nest of a very poor design. I cannot believe I spoke to the designer (Mikail??) a few years ago and how badly I wanted one of these amp. Has anything changed? Did the OP somehow receive a prototype model? What's the top (non-Chinese) tube amp these days that a serious listener should consider to drive my AKG 701 and HD600 phones?

Nothing has changed.... do not buy SinglePower amps. A large number of them have had problems... the one that I owned died. I am sure that many more have taken a nose dive or will in the future if they are not fixed before major (very dangerous) problems arise.

Eddie Current and Woo Audio have very good (tube) products and are both located in the US.

 

[PhilS]

Here's an update on my Supra. I had Wayne at Bolder Cable re-work a few things to make the amp safe. It took a little extra time, as I had to send Wayne the various adapters and tubes I had so he could make sure the amp worked in all configurations.

I received it back yesterday and spent some time listening to it last night. It sounds terrific. Actually, it sounds a little better than it did before, and I was already very pleased with the sound of the stock unit. With Wayne's modifications, it has a little more punch and a little more bass, which really helps my favorite cans, the K-701's.

I really wanted to save this amp, and am really glad that I had it "made safe." I was worried a bit about whether the sound would materially change from what I had enjoyed previously, but, as I said, the only changes are for the better. Thanks Wayne.

 

[Skylab]

That's nice to hear, Phil. Welcome to the "Safe Singlepower" club

 

[mrarroyo]

^ That sounds almost like "Safer S_x"!

Sorry I could not resist.

 

[Skylab]

I'm glad someone got the joke

 

[vhbaske]

Hi guys, try to spill some water on a tube.... another grenade! For me, I don't like tube amps. I lived in the era when everything was in tubes, I personally disliked them. I know this is no thread for tube dislikers (haters?) buy I have my reasons. I remember every amplifier having too much distortion when volume pot was in 1:00 and 3:00 you cannot pass over there, you heard a French horn blown by a kid. I have seen many tube amplifiers with the tubes hanging outside as to display them. Be very careful. Oh, and I forgot thunders, many thunders exploded tubes of many radios and television sets. I am here in Puerto Rico. I am not too old (56 years). I stay away from tubes. Assemble a M3. Don't get mad at me, just consider my reasonings. Thanks to all of you in advance.

 

[kevin gilmore]

The change in sound quality vs pot position is well known and happens to
both solid state and tube amps. If you don't want that to happen, you need
a constant impedance step attenuator.

 

[mrarroyo]

I am a tube lover, and thanks to Dr. Gilmore for the hints he provided so I could fix my MPX3 is sounding beautifully. Thanks again Kevin!

 

[Skylab]

That is great, Miguel.

 

[Bolder]

I just finished looking at a MPX3.

This one has the high/low voltage switch that is rated at 25 volts. No balancing resistors. Black Gates on the HV section. A couple of Russian Teflon caps and this:

An under $30.00 power transformer. This amp was running a pair of 6BL7GTAs for outputs and 6SN7 for driver. Now that adds up to something like 3.6 amps for the filaments. This transformer is rated for 2 amps.

No wonder the filament circuit looked like this:

 

[kevin gilmore]

These high voltage models are especially dangerous. Without the heavy
and overloaded filament to suck power out of the transformer, the high
voltage exceeds the voltage ratings on the power caps by about 75 volts.

The most that should be in any of the mpx3/ppx3's is a 500 VCT unit
with 6 amperes of filament current.

 

[mattigol]

I do not know if the following information is of much use to any 230V dwelling head-fier, but I'll post it anyway: Back in 2005 I bought a used 110V US spec PPX3-SN7 which was then factory-upgraded to the SLAM version (received a circuit board instead of the point2point wiring it had before). Due to an irritating hum of the stock power transformer in conjunction with a step-up tranny, which caused vibrations of the whole chassis, I was soon looking for a solution. A ground loop wan't the problem. I wasn't willing to shell out 400 US$ for a 230V Plitron transformer, so I got some specs from Mikhail and bought an oversized 230V toroideal here for a fraction of the Plitron. The upgrade, which I performed myself, went well and the amp has been working flawlessly for 4 years now. Luckily I did not encounter any overheated parts that have been posted in this thread. The tranny is top-notch in terms of quality and workmanship, dead-quiet too, runs cool to the touch even over prolongued periods of time. Transtec supplies trannies to brands such as Berendsen and Einstein. In hindsight, had I had any idea at the time of the dangers involved in working inside this particular amp, I wouldn't have tried it. Maybe this helps someone who is trying to fix his amp over on this side of the pond.

 

[fongalv]

Hi guys,

Been away for a couple of months and came back just to see this...mine is an MPX3 Slam, and I've included some pictures of the innards I took while cleaning the amp 2 weeks ago, no visible staining or bulging caps. I have no issues with it under regular use until now that it has become a potential IED...

Anyone kind enough to visually check it through for me? Did'nt check the specs of the transformer and I won't be home till next year to check on it(mines 220V btw).

Thanks in advance!

 

[HeadphoneAddict]

You need to include pictures of the power supply, including the uncovered transformers. Then the experts can chime in about how everything looks.

 

[Frihed89]

This is the older board. There was at least one subsequent revision: C in Aug 2006. I am not sure if anyone has compared them, but the newer board has 2 layers with the tube sockets on the top layer Underneath. You still have the vastly under-rated high power switch and no bleeder caps across the two large PS caps. The advice I got here was to bypass the hi-low power switch and hard wire it as low voltage only all the way and just forget about the high power option. The bleeder resistors are also talked about here and are an anti-shock safety repair. The 4 diodes in the lower right and the 2 in the upper right have been way undersized in some rigs, causing discoloration to the board. It's hard to see this discoloration, so look carefully for small changes in the color tones just around these diodes, moving in the direction of yellow/brown. Miguel's various contributions cover how to fix the ones in the lower right. (But since you have no discoloration, maybe they are OK?) Also, if you are using the Supra Power supply, some of the MPX3 Slams with the new board had 2 extra electrolytic caps right next to c58. I am not sure what these are about.