Conrad Johnson PV12 AL

The PV12 used a 3 stage power supply. A pre-regulator fed a separate regulator for each side.

In addition to putting in better caps, or bypassing existing, adding some heat sinks to the regulators (really just transistors) could be useful in increasing reliability.

Also the resistor used in the power supply CRC circuits could be improved.

I’m really not a fan of mixed-metal conductors though.

Best bang for the buck on those is really the output caps though. They make much better caps than the PV10/12s had. If you are a noob, start there. :) Watch the cap voltage ratings carefully though.

Best of listening!

Erik

Yes, you may very well need to stand them up.  Depends which direction you go. :)

Plan on standing them up and adding an extension.  So, a little soldering, and maybe a little heat shrink, with some solid copper core.  Also will need a dab of hot glue. Don't go nuts, in case you want to change things later.

Honestly, having done this before, I would encourage you to just do the output caps and stop there. :) After that it's a lot of diminishing returns, but those two caps can really do a lot.

Best,


Erik

Forgot to mention, Chris Johnson (previously of Sonic Frontiers) at Parts Connexion has a lot of experience with this, send him an e-mail after you acquire your victim, er, preamp.  He'll give you great suggestions, and may even give you a discount on caps.

Best,

Erik

@orpheus10 Sorry for the delay.

For the PV-12, there are 2 sets of caps which are really key. As I wrote before, the output caps are really most critical If they are 2uF, upgrade them to 4uF, maintaining or exceeding the original voltage. Alternatively use a pair of 2uF caps on each.  How crazy you want to go is up to you. The sky is the limit in your spending.

After this there is a large electrolytic which I believe is on the heater or something like that. It basically just maintains a DC voltage to the tubes, but it’s part of the signal instead of the DC supply, so it’s not fed directly by the regulators.

After these two, the PV-12 (if memory serves) has a 2 level voltage regulation stages. A pre-regulator, and then 1 more per channel. You can identify the stages by the chain of zener diodes in each.

Don’t go too crazy, but it may be worth replacing or bypassing the filter caps on the outputs of each of these 3 stages. Save your money for the output caps though!

Lastly, add heat sinks to each of the transistors used as regulators. They go out frequently and sinks are cheap. :)

One more advanced mod which I never did and now don't remember is to lower the total gain. That preamp has too much gain, and you don't need it.  Lower the gain and you'll get much less noise.