The Amp Garage

Once you have an arc occur there may be carbon tracking on the tube sockets which must be completely removed to prevent more arcing. If the socket material has been burned, replacing the socket may be necessary. So what caused the initial arcing? I think it was most likely an oscillation in the pow...

Spent the morning putting a PT from Mojotone in. Now the B+ is 458vdc in standby. Put it to Operate and saw a MAJOR arc in V8 and inside the amp at the same time. V8 heater opened and evidently shorted to B+. Cut the power immediately. Both 100 ohm heater to ground resistors smoked. Replaced 100 ohm...

Hi Glenn Apologies if this is me being stupid. Given that the #102 is providing 428V with a 340-0-340 @400mA PT isn't it reasonable you'd get the lower B+ reading of 414V from the 320-0-320 @450mA PT in the SSS with the same wall voltage? Could it be the higher 440V reading you noted was taken unde...

I had the same problem in one amp, when inside the box.. chassis and power transformer were extremelly hot.. while outside on the table, chassis and PT temp was just moderate, nothing to worry about... Then i discover that there is no sufficient air circulation in the cabinet, and tubes were heatin...

102 amp is still on, Operate, idle-no input. Transformer is very warm, I can only keep my fingers on it for 2-3 seconds. Similar in temperature to SSS transformer. This is after nearly 4 hours operation.

I just checked voltages on my 102 w/built in Dumbleator that has basically same PT and 6L6 power tubes.

B+ in operate is 428vdc
Power tubes biased to 42mA
Wall voltage 119vac
Secondary voltages in operate 333-67-0-333vac

Hasn't been on long enough for PT to reach stable temperature.

I only have one fuse, 3 amp slow on input power.

In Operate

118vac wall voltage
320-0-322 vac secondary. 320vac leg is also feeding bias circuit.

B+ 414vdc

Bias -360vdc at 5mA

PT's biased to 27mA with -49 volts.

Does anyone know if Heyboer will rewind one of their transformers for a fee? I’m thinking it would probably be cheaper to buy a new one. Interested to know if you find out. I agree it would likely be more. More work because they must remove the old windings and disassemble core prior to winding. I ...

Great looking build Glenn - your son is lucky indeed. Does the PT get that hot in standby? I wonder if the PT buzzing earlier on in your process was more sinister than it seemed. Mine doesn’t run hot, but is a 2x6L6 with tremolux iron. Might be worth tracking your wall voltage too, just in case tha...

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...