GM-70 Amplifier

[David McGown]

Terrific, Dave! Glad you were able to put that iron to good use!

Grover,

Thanks, and finally! I haven't had much time for amp building with work and my music endevours, and it has been a very long time from conception to execution. Not sure how many more amps I will get around to building once I get these finished, so need to make sure that the other iron I have of yours gets distributed among the local DIYers to be a part of their projects.

So when I have a meet to show off the new amps in the next few weeks, I will have a iron (and parts) giveaway to clear out stuff I am just not going to get around to using. I know Mary will be happy to reduce the clutter.

David

[Guy]

I know Mary will be happy to reduce the clutter.

Nawww, Mary doesn't mind the storage!

[David McGown]

Made good progress last night, power supply wiring nearly completed, output transformer fully wired to GM70 plate and amp output terminals, Coleman current regulator installed, just need to wire up the driver (including finishing the power supply) and the GM70. Looking like I may have this done by the weekend!

Attachments

[J-ROB]

We po' folks use 3m copper shielding tape for ground busses.

[David McGown]

Finished the second amp and both now in the system. Now the break-in process. Highs are slowly coming in, but the amp does have quite a sense of authority. I do not need subwoofers.

Attachments

[David McGown]

Tip for the next time. Check direction on bifilar wound interstage transformers. I was wondering why the amp was so rolled off on top and boomy. Reversed leads on one winding and now it is sounding right.

David

[SoundMods]

OOPS! I've been there and done. The Devil is in the details.

[David McGown]

Yeah, I won't do that again.

Man, these amps do Shostakovich!

David

[Guy]

Another sonic experience! How will they sound in a week?

[David McGown]

Another sonic experience! How will they sound in a week?

I am looking forward to the break-in. They already are better than my 300B DRD SET amps I have been listening to for the past three (or so) years. The things I am noticing are that instruments sound real, with a harmonic complexity and presence, a greater sense of spaciousness, and lack of strain in dynamic peaks. I am sure once I recover from all the excitement, I will find problems to fix. I am already working on fixed bias supplies to add to replace the cathode resistor and cap bypass (which I did initially just to get the amps working). But I will let them break in for a while before adding this feature.

David