The Amp Garage

Swapping the OT primaries solved it! Thank you to Stevem and xtian for your help! There's another issue somewhere in the preamp because the audio signal isn't making it all the way through, but I think that's just either a bad tube or the conductor in my shielded wire is getting shorted to ground. I...

Well Its time to start removing tubes to deactivate circuits and then replace them one by one. Yank them all out but for the output tubes, do you still then have the issue? I pulled all the preamp tubes and started putting them back in, going backwards from the PI (V4), and the noise returned when ...

After looking at some wiring layouts, last night I moved the grid stoppers right onto the power tubes. I did the same for V1. Now the noise at the output is a steady 86.27Hz at 75Vp-p. So... progress? :lol: First thing I tried was removing the NFB but the noise persisted. I have yet to start popping...

93 volts P to P is over 1000 watts into a 8 ohm load, so your 300 watt load resistor should be burning up! Is that the case? I try not to let oscillations, especially of this magnitude, run for too long while I'm testing so I haven't really noticed the load getting very hot. I only run it for maybe...

A few months ago I posted about converting an Ampeg V5 to a Hiwatt DR103. You can read the post here if you'd like. Quick background: My friend/guitar player in my band bought an Ampeg V5 in hopes of having a cool variation on a 2203 circuit but we found out after purchasing (Reverb) that the previo...

mhuss wrote: ↑Mon Jan 30, 2023 6:20 pm Sounds like a good project. I don't have any objection to any of your bullet points.

Best of luck with it.

Thanks and thank you for the schematics on your website that I referenced!

Quick background: My friend/guitar player in my band bought an Ampeg V5 in hopes of having a cool variation on a 2203 circuit but we found out after purchasing (Reverb) that the previous owner had totally gutted the amp and modded it beyond recognition with all new iron. Rather than make it just an...

I'm a regular customer of Tube Town and I even used the mentioned set of transformers in a bass amp with pleasing results. In my opinion Tube Town is a very serious store without all that voodoo / snake oil stuff TAD will tell (and charge) you. Thank you for answering my question directly! I really...

I'm building a Hiwatt DR103 type of amp for my friend/guitar player in my band. We're into big, loud amps and I've been curious about KT88 tubes so I'm thinking about sticking a DR201 OT in the amp and using 4X KT88s to get 200W out. The price of a DR201 OT from Tube Town is pretty good at 110 EUR ,...

...Anyway, I have put a 4.7K resistor across the standby switch ... Merlin suggests 47k, but as your HT voltage is so high, I’d increase that, eg 100k. Thank you for pointing this out because I was just going to post how when the standby switch is opened the HT only drops to about 475V and doesn't ...

Phil, I see your rationale, but I think it’s standard terminology for a switch, when ‘closed’, to allow current to pass, and for it to stop current flow when it’s ‘open’. Other common switch terminology is ‘make’ and ‘break’, perhaps that’s a bit less open to misunderstanding? Basically, in every w...

I guess maybe the terminology is confusing me. Closed in my head meant 'shut off' The scope seems to show that the voltage dropped drastically, spiked a few times, then dropped again, like caps were discharging and then the voltage was gone. Since there's no mark of what the actual bottom and top v...

pompeiisneaks wrote: ↑Thu Apr 08, 2021 5:31 pm I'd think seeing when it opens is more helpful, as the spikes likely come when an amps caps are pulling large inrush current to charge up, but maybe I've misunderstood the potential fault?

~Phil

But aren't the caps charging when the switch closes, not opens?

Here's a measurement of the cathode of D5 while the the standby switch is being closed. This was done with a 100X scope.

If it was PIV related then some options could be to use 2x 1N5408 or UF5408 in series, and add a C-RC snubber across the HV secondary, and replace the standby switch if the amp has been in service for some time (as the contacts may have degraded). I don't think I can fit double the diodes, but I'm ...