A SSS Build

[GAStan]

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 caps as suspects. To me this points to the PT, but I can't explain why the outputs are still balanced if it had some shorted windings.

[GAStan]

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 caps as suspects. To me this points to the PT, but I can't explain why the outputs are still balanced if it had some shorted windings.

I'm a dork. The above readings were all AC. With meter set to DC initial power on is momentary 10-20mA dropping immediately to 1-2mA. To Operate it peaks about 1 amp quickly dropping to and maintaining 150mA.

[GAStan]

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.

[GAStan]

Here's the B+ ripple.

20240518_141512.jpg

[GAStan]

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 ohm ESR @ 100hz. Powered up amp while 47uF caps were disconnected and it again settled at ~420vdc.

Still can't figure out why B+ is now 25 volts less than it was yesterday.

Going to let it burn in several more hours and monitor voltages periodically.

Does anyone have any suggestions, theories or troubleshooting tips to offer?

[timrobertson100]

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 that’s drifting around.

Other than the voltage change and hot PT, is it still working?

[martin manning]

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).voltages periodically.
Still can't figure out why B+ is now 25 volts less than it was yesterday.
Does anyone have any suggestions, theories or troubleshooting tips to offer?

I’m afraid that the PT may have been damaged in the initial power-up.

[GAStan]

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 that’s drifting around.

Other than the voltage change and hot PT, is it still working?

Thank you Tim. I have not left it in Standby long enough, but I will try this to see. I'll try it.

Wall voltage does vary a few volts, 119 to 122 is what I typically see, but 120 is what i normally see.. Currently 122vac wall voltage resulting in 430vdc B+ in Operate.

Yes it is working despite what you mention, but voltage seems to vary a bit each time I power it up. I've decided that if I can get consistent voltages I'll adjust dropping resistors accordingly. If not I'll spring for a new transformer.

I’m afraid that the PT may have been damaged in the initial power-up.

I'm beginning to think this too.

Does anyone know if Heyboer will rewind one of their transformers for a fee?

[martin manning]

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.

[GAStan]

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 just ordered a new identical transformer. I'll keep this old one and probably use it for testing and/or cap forming.

Currently amp is 118vac wall 415vdc B+.

[martin manning]

You could do a shorted turns test on the one you have. See https://ampgarage.com/forum/viewtopic.p ... 11#p445611
Or if you have a power meter you could try energizing the primary with everything disconnected.

[bepone]

Hmm it is strange thing.. Does PT has normal voltages in operation? Pls retest IN OPERATION all the voltages, and write here.. If they are normal, and current consumption is normal.. And transformer is hot.. then is undersized for this application..

[bepone]

Usually power transformer is last thing to fail..almost impossible in good wound transformer.. Also fuses should be burned before the transformer..

[GAStan]

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.

[GAStan]

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.