The Amp Garage

Replaced rectifier diodes, no change in how it acts. B+ back up to 420vdc range with +/-2vdc drift. Transformer too hot to touch more than a few seconds, maybe 110°F to 120°F. PT's biased to ~15watts (36 mA @ 420 volts). Isolated and checked 47uF 500v caps before Standby switch. Both test 50uF and 1...

Here's the B+ ripple.

B+ is now down to 411vdc in Operate. Voltage out of PT is still 320-0-320vac. I think this rules out the PT as issue. Rectifiers? I used UF4007, 6 of them. I've got plenty so will replace them.

I'm open to suggestions.

Checked B+ current. In Standby at initial power on peaks at about 50mA then drops to 4mA. I suspect it would continue dropping as the caps charged but I was impatient so went to Operate. Peaked about 1.25 Amps then dropped to 255mA and held there +/- 5mA. I think I can rule out the first two 47uF c...

Checked B+ current. In Standby at initial power on peaks at about 50mA then drops to 4mA. I suspect it would continue dropping as the caps charged but I was impatient so went to Operate. Peaked about 1.25 Amps then dropped to 255mA and held there +/- 5mA. I think I can rule out the first two 47uF ca...

Today powered up the SSS to get voltage readings and found that the B+ has dropped ~25vdc. In standby it was 468vdc, now it's 440vdc. Taking it out of standby to operate B+ drops to 420vdc. Transformer AC out is 328-0-328 in Standby, 320-0-320 in Operate. Not sure what's going on, voltages were good...

jabguit wrote: ↑Sat May 18, 2024 10:47 am

GAStan wrote: ↑Thu May 09, 2024 12:45 pm Found these at Grainger.

But...the invoice is from McMaster......

My bad. I'll fix it, thanks for pointing it out

Nearly finished, just need to build the pedal and its cable. The amp itself works great! Finished the amp last night too late to power it up. This morning I used my variac to slowly bring it up sans tubes. Spent several hours bringing it up slowly giving the caps some time to form. First I put 12vac...

What would you recommend as a starter amp? Would it be a better learning experience to start with a kit or with a full build? Have you had a look at Rob Robinette's site ? He has a lot of info on building amps, you might find a good first build there. My first build was a kit from Mojotone, their S...

Roe wrote: ↑Sat May 11, 2024 9:39 am Looks great. and reminds me that I have a cab and chassis and lots of NOS 7581as waiting (need transformers)

Thank Roe. You've done what I intended-put the chassis away for a while and slowly acquire the necessary parts. Guess I'm too impatient...

Just clicked these pics. The last pics I posted were actually a few days old so this is the result of a few days work. 20240510_202417.jpg 20240510_202436.jpg 20240510_202451.jpg 20240510_202504.jpg 20240510_202519.jpg Tomorrow, after a good once over, I'll most likely begin on the transformers.

Second, there is a distinct "electrical" smell coming from the area of the power amp part of the chassis. Everything seems to measure normal and visually appears normal. So not sure about what is going on with that. Will work on biasing the FET next. -Dan Try looking for any arcing in a very dark r...

Just a word of caution on these piher balance trimmers. If they sit for a long while not having been moved, they can develop an oxidation and non-conduction over time when you do move to a new setting. This just happened to me on an AB165 build where I had implemented that balance trim put for the ...

Nice! This motivates me to pull out my empty Erwin chassis too and get to work. What are the relays going to switch please? On my previous Erwin-sourced chassis I found those wing nuts stripped super easily after a couple of uses. I ended up drilling out slightly larger holes and using normal chass...

Here's what the build looked like a few days ago. Heater wires done, working on power tubes. Mounted 12v transformer for relay power. Whe I went to mount the 12v rectifier board found it wouldn't fit, caps were too big and interfered with PT. Ordered some physically skinnier caps, now waiting for th...