6N2 swap

[tvrgeek]

OK, I know there were some posts on the MENG 6P1 amp , but darn if I can find them. Anyway, new to fiddeling with tubes, more of a digital background. Bought one of these cheapies. Not bad for the price, but still quite harsh. The 6N2's have a pretty bad rep, so planing on putting in 12AX7's as 6ax7's have not existed for 40 years. If I read it correctly, I need to disconnect the pin 4 or 5 from the PWB so I can tie 4 & 5 together on the socket and tie pin 9 to the other input.

Do the blue LED's stuffed into the socket have any function at all? ( in parallel witht he heaters.)

I can see a few other mods, like a line fuse, at least twisted if not shielded input lines, add a second set of inputs and s switch. The B+ caps could easily been enlarged and maybe add chokes. Guess I should have picked an old point-to-point chassis to play with.

[Arnulf]

Originally Posted by tvrgeek

If I read it correctly, I need to disconnect the pin 4 or 5 from the PWB so I can tie 4 & 5 together on the socket and tie pin 9 to the other input.

This is correct, pin 9 is the center point of the (12.6V) filament so you need to put both sections in parallel for 6.3V operation.

Do the blue LED's stuffed into the socket have any function at all? ( in parallel witht he heaters.)

Schematic ? I can't think of any use for them but it's hard to say without seeing the schematics.

[tvrgeek]

Found a couple of NOS 6ax7's. Think I'll start there. Made a long list of things I'd like to try. Very simple amp, just a long-tailed splitter and a push-pull output. Feedback off the secondary to the splitter.Textbook. Not sure where it is biased or what the total gain is. Funny they sell it as an "integrated" amp when it does not even have a front end buffer or gain stags. Just a cheap pot. Not a lot of extra room but enough to play. So, need to do some benchmarks while waiting for the tubes.
Gleaning the available literature, the ideas that may have technical merit:

Replace the splitter tubes. It these change the sound a lot, may try different ones
More B+ caps. Every amp needs more B+ !
Play with compensation in the feedback
Isolation diode in the B+ separating the splitter from the outputs
CCS in the outputs
Grid drain ziener
DC filaments
B+ regulator if I have enough margin
Remove volume control and the long unshielded leads.
Add a use in the AC line. ( scary!)
Input cap. It has none. Yea caps are bad, but a little DC on the input is a good way to loose some tubes.

That should get me familiar with tubes. Then maybe I can make my HK A 300 sound better. I was very disappointed when I fired it up. At least it was free.

[Kung]

Thanks for sharing. It's great.