The Amp Garage

pdf64 wrote: ↑Mon Jun 07, 2021 5:43 pm It seems strange that the root cause was something in the phase splitter, yet the presence control setting didn’t affect it.

Yes, the presence control did change the issue along with the treble control

As an update. I have a pile of papers here on my bench and many of the schematics layouts diagrams for all the hiwatt models - and missed that the phase inverter on the early 70's Dr103 is a 12at7, i had a 12ax7 in there. I have now put in a 12at7 and the amp has zero oscillating..... As something ...

As an update.

I have a pile of papers here on my bench and many of the schematics layouts diagrams for all the hiwatt models - and missed that the phase inverter on the early 70's Dr103 is a 12at7, i had a 12ax7 in there. I have now put in a 12at7 and the amp has zero oscillating.....

This is what i have found online from Mhuss.

pdf64 wrote: ↑Thu Jun 03, 2021 7:19 pm So the presence control setting doesn’t affect the issue?
If so, that kinda indicates that the power amp isn’t in the loop.

Yes! You are correct, the presence control does mute the issue with the pot all the was Clockwise just as the treble pot.

Thoughts

I am fine with you deleting it - the other members have provided some great insight and idea that may help others. Can you combine the threads?

Thanks Phil,

Please keep the post located in The hiwatt Group and remove from the other area.

Here is a picture of the build

Hello everyone, I built a a Dr103 clone and it all works and sounds great except for the master volume oscillating between 95-100% clockwise. The amp only oscillates when the MV pot is all the way clockwise - . What mitigates the oscillating is with the mv FCW and the treble FCW as well. With the mv...

Steven - yes they are. Mil spec. On measuring an original they all came in at under 22k - i ran out of 22k resistors and used 1 watt 21.5k Mil spec, measuring the same as the original.

I just want to be clear - the amp only oscillates at maximum on the master volume, turn it back 10 percent and its gone. If I turn the treble all the way clockwise with the master all the way clockwise there is no oscillating. With the plate leads oriented wrong the amp will oscillate instantly. It ...

Thanks for all your replies. Yes I kept the wires long until first fire up to determine the orientation. Here is a picture of it now. My first instinct is a bad wiper on the mv pot as I have run into that sound before. There are a lot of pictures online of the Dr103. I use it all when i build, pictu...

Thanks for your reply Phil if you can view my photo, I kept the blue wires long at the board until I knew they were oriented correctly. That noise is unmistakable

Hello everyone, I built a a Dr103 clone and it all works and sounds great except for the master volume oscillating at max. What mitigates the oscillating when the mv is maxed is with the treble at max as well. If I have the mv all the way clockwise and the treble all the way clockwise the amp functi...