What should be mod first in my amp

[andy2]

I just recently bought a Ming Da 300B -4T amp and would like to do some mods. The amp uses 2 300B tubes in push pull which puts out 22W per channel.

I am thinking of changing all the coupling caps first. Currently the amp uses all Solen .47uf. I want to change them all to Jenson PIO copper since these caps have sort of a musical sound.
Next I would like to replace the resistors that connect the driver stage to the output stages.

Here is the picture of the am internally.
http://www.geocities.com/hai_vu1/mingda.JPG

Can someone tell me what those diodes on the upper left corner? They look to me like some kind of voltage doubler? I heard that you can change those diodes to some sort of "fast recovery diode". Can someone tell me where I can get those diodes? Is it worth it?

 

[SHiFTY]

Nice Amp! Easy to work on, however I would spend the money on some NOS (or even used) input tubes. You can usually hear the difference, not to mention see it! Also some 300B mesh plates would look awesome.

As for the diodes, that does look a bit like a voltage doubler using 1N4007s. I prefer to use 1N5408, the much gruntier cousin, which can handle lots of abuse. However the stock ones are probably adequate and I doubt you'll get much benefit from changing them. Especially UF4007 are a bit fragile- some shorted on me once. Same goes for resistors- more trouble than its worth IMHO.

The other thing you should look at replacing is the cathode bypass caps on the output tubes- they definitely influence the sound. Maybe replace the Solen coupling caps if you like, I personally find them OK. Some people have said the Sprague orange drops are better than the Solen, I couldn't hear the difference. Any of the mega dollar caps are a bit of a waste of money IMHO. Better to buy some good tubes...

I like how this amp has 220K bleeder resistors across the PS caps... Nice touch! However, usual rules about safety apply, read teh safety thread etc.

 

[andy2]

Nice Amp! Easy to work on, however I would spend the money on some NOS (or even used) input tubes. You can usually hear the difference, not to mention see it! Also some 300B mesh plates would look awesome.

As for the diodes, that does look a bit like a voltage doubler using 1N4007s. I prefer to use 1N5408, the much gruntier cousin, which can handle lots of abuse. However the stock ones are probably adequate and I doubt you'll get much benefit from changing them. Especially UF4007 are a bit fragile- some shorted on me once. Same goes for resistors- more trouble than its worth IMHO.

The other thing you should look at replacing is the cathode bypass caps on the output tubes- they definitely influence the sound. Maybe replace the Solen coupling caps if you like, I personally find them OK. Some people have said the Sprague orange drops are better than the Solen, I couldn't hear the difference. Any of the mega dollar caps are a bit of a waste of money IMHO. Better to buy some good tubes...

I like how this amp has 220K bleeder resistors across the PS caps... Nice touch! However, usual rules about safety apply, read teh safety thread etc.

Thanks for the tips.
Here is the plan:

1. Replace tubes to NOS
2. Replace coupling tubes to Jensen PIO
3. Replace Cathode bypass caps.

then will see ...