[davehanc]

Just about finished putting #2 together, but after about 20 hours use #1 has gone silent. None of the 6H30 tubes are glowing (5AR4 looks OK), and there's nothing across M+ and M- to measure - suspect a power supply problem, possibly a dry joint?

I'd appreciate advice about where to start measuring and troubleshooting.

Thanks
David

[hagtech]

Is the LED ok?  Sounds like you lost heaters.  Check for 6.3Vac on heaters of 6H30s.  What is B+?  What is dc voltage at M+ to ground?

jh

[davehanc]

LED seems OK - from a cold start, begins turning green about 20 seconds, full green about 25 seconds
6H30 heaters 3.0Vac
M+ to ground no dc voltage, with any position of balance pot
I don't know where to measure B+ - can't see a reference to this on the board or in the schematics?

Thanks
David

[hagtech]

Power sounds ok.  Heaters will measure 6Vac across pins 4-5, or 3Vac from either pin to ground.  

The red wire on output tranny should be about 200Vdc.  Also, what are dc voltages on blu and brown wires?

Do you have any way to check tubes?

jh

[davehanc]

6H30 - Pins 4 & 5 (counting clockwise on underside of PCB from gap) both measure 3Vac to ground. There is no voltage across pins 4-5.

Output Tranny - Red, blu & brn to ground all measure 357Vdc.

I have no way of checking tubes, apart from swapping in new ones trial and error. Probably not a good idea just yet, given these numbers!

Thanks
David

[hagtech]

Ok, we're getting somewhere.  There should be 6.3Vac across pins 4-5 on all of the 6H30s.  I think one of the green wires from tranny is broken.  That's the only thing that makes sense to me.  See if you can track that down.  Any burned heater traces?

jh

[davehanc]

No sign of any burnt traces. I'm listening to the amp as I type this - though I'm unsure just how and when it started working again.

I checked both power tranny green leads out of circuit, and both measured 3Vac to ground. I resoldered them to the spade terminals (I didn't use crimps), and noticed that with only the one which leads to D1L & D2L connected the LED was OK; with only the other (to empty D1R & D2R) connected it didn't light up. I connected both green leads and started to look for 6Vac between the traces and found it only at the green leads. Started wondering whether both C6L & C6R should be installed (as per the parts list and the illustration in the manual - I don't see it in the schematic?), and noticed the 6H30 tubes were glowing.

I'm measuring in circuit:
Power tranny green to green 6.2 Vac
Both green leads 2.9Vac to ground
Across heater traces at empty D1R/D2R location 5.7Vac
Output tranny Red to ground 186.5Vdc
Blu to ground 180.8Vdc
Brn to ground 181.3 Vdc
6H30 pin 4 to ground 2.8Vac
pin 5 to ground 2.2 Vac
pin 4 to 5 5.5Vac

Most numbers look a bit on the low side, but it is working and sounds good. Any next steps?

Thanks
David

[hagtech]

Voltages seem low.  What is your ac line voltage?

jh

[davehanc]

Line voltage is 240Vac (243 at the moment).
I finished assembling #2 this afternoon, and it measures a bit higher - 6.0Vac across pins 4 & 5, and 2.8Vac from either pin to ground.

Thanks
David

[hagtech]

What voltage do you have at M+ or M- to ground?

jh

[davehanc]

#1 M+ and M- 11.77Vdc
#2 M+ and M- 12.06Vdc

[hagtech]

Good, but they're a touch low too.  Everything seems to be down about 8% or so.  That's ok, I suppose.  Just odd.  Any other 5AR4's lying around to check?

Are you able to balance the output section with R28?

jh

[davehanc]

Yes, the DC balance was staightforward. I have no other 5AR4s, but wouldn't mind trying another pair if only for curiosity. I'm using Sovtek, but can source locally JJ/Tesla, Golden Dragon and a few others - any recommendation?

I'm pretty sure my original problem with the heaters was a high resistance connection on one of the power tranny green leads - it hasn't occurred again since resoldering.

Thanks
David