#002 - my journey begins

[Bombacaototal]

So the new bias cap is giving the right voltage, but when the previous one failed the excess of current likely took out something else . Tube, screenresistor? Also the things Richard mentioned should be worth checking.

Thanks Erwin, I did measure all voltages and diodes and fuse (after replacing the previous) and everything is fine. I will replace the screen resistors, but will need to get new standby switches. I am concerned to try with the current tubes, probably a good idea to get a new set in?

Any other potential failing items? I think that should cover right!?

I am also thinking that if screens were bust should I have issues at first start up as well?

I think as well I took time between the two and four tubes start and probably B+ had gone down and why I had no issues?

Also wondering why my mains fuse is not going. I have it very low at 1.5A, shouldn't it be popping as well?

[Richard1001]

OK, not so good. I turned on and off and when I turned on again, I head a hum and saw the PT HT fuse go. I was monitoring C- and had -356V, so not there the issue

Standby Switch is gone again. Back with 2 power tubes and seems fine. Will test further. Probably a bad power tube (one of the two I removed?). Bias seems fine at 36/37mA on the two tubes. Voltages seem good across as well

EDIT 1: So I turned on and off again and heard the hum again (turned off imediately) but C- was in rage at -350V. Any idea of what else may be causing the PT to pull so much current?

EDIT 2: Power tubes all out again, and all voltages look fine. To me its clear that on first start it is fine, but if I shut down and bring the amp back up, the tubes already have the B+ and this is where there is the issue

What is the value of the fuse? mA? Fast or slow blo?

Using the standby switch will pull much current. Because the two 100uf caps have low ESR they will pull a short but high load current. The 47uf caps will essentialy see a short circuit when the standby is turned on. Both the 47uf and 100uf caps will not be happy. Some hum when switching on is normal in the given schematic. I actualy think there is a mistake in the powersupply schematic. Either a part missing (Reactor coil) or the switch drawn in the wrong place. But this should not make your amp fail like it does.

Turning the amp on from standby, the power tubes will also pull high current for a moment. Could be there is a bad power tube that does not recover from this.

It is also important that the CF tube can take the high voltage (420 + 45 bias = way over the data sheet specs) The McIntoch amp this CF design was copied from used a Telefunken ECC83 tube. Both triodes will have close to 1mA plate current. Maybe try a different one. Sovtec tubes van take much abuse.

But first thing would be checking the value of the fuse.

[Bombacaototal]

OK, not so good. I turned on and off and when I turned on again, I head a hum and saw the PT HT fuse go. I was monitoring C- and had -356V, so not there the issue

Standby Switch is gone again. Back with 2 power tubes and seems fine. Will test further. Probably a bad power tube (one of the two I removed?). Bias seems fine at 36/37mA on the two tubes. Voltages seem good across as well

EDIT 1: So I turned on and off again and heard the hum again (turned off imediately) but C- was in rage at -350V. Any idea of what else may be causing the PT to pull so much current?

EDIT 2: Power tubes all out again, and all voltages look fine. To me its clear that on first start it is fine, but if I shut down and bring the amp back up, the tubes already have the B+ and this is where there is the issue

What is the value of the fuse? mA? Fast or slow blo?

Using the standby switch will pull much current. Because the two 100uf caps have low ESR they will pull a short but high load current. The 47uf caps will essentialy see a short circuit when the standby is turned on. Both the 47uf and 100uf caps will not be happy. Some hum when switching on is normal in the given schematic. I actualy think there is a mistake in the powersupply schematic. Either a part missing (Reactor coil) or the switch drawn in the wrong place. But this should not make your amp fail like it does.

Turning the amp on from standby, the power tubes will also pull high current for a moment. Could be there is a bad power tube that does not recover from this.

It is also important that the CF tube can take the high voltage (420 + 45 bias = way over the data sheet specs) The McIntoch amp this CF design was copied from used a Telefunken ECC83 tube. Both triodes will have close to 1mA plate current. Maybe try a different one. Sovtec tubes van take much abuse.

But first thing would be checking the value of the fuse.

Thanks for the help Richard

The mains fuse is 1.5A, 250V, slow blow. The HT is 500mA, slow blow

Do you have any suggestion on how to improve this standby? Attached the #121 power section, amp which uses the same SVT style power amp with the CF and the standby seems at the same place

I just bought a quad of TAD red plate. Maybe safe to wait for them before proceeding? I am concerned my power tubes may be gone. I may probably pull the CF out for the first trial with the new tubes. Any further suggestions?

My CF tube is a NOS Tungsram ECC83 (V46) Short Plates Halo Getter. I can try another one but probably with new power tubes?

[Bombacaototal]

So my amp has the standby failed, so its same as not having it. I have pulled the CF tube out and turned it on with two central power tubes.

Seemed all fine, checked voltages and all. Turned off, waited a bit and on again, no issues again.

Could all this come down to my CF tube?

[Richard1001]

OK, not so good. I turned on and off and when I turned on again, I head a hum and saw the PT HT fuse go. I was monitoring C- and had -356V, so not there the issue

Standby Switch is gone again. Back with 2 power tubes and seems fine. Will test further. Probably a bad power tube (one of the two I removed?). Bias seems fine at 36/37mA on the two tubes. Voltages seem good across as well

EDIT 1: So I turned on and off again and heard the hum again (turned off imediately) but C- was in rage at -350V. Any idea of what else may be causing the PT to pull so much current?

EDIT 2: Power tubes all out again, and all voltages look fine. To me its clear that on first start it is fine, but if I shut down and bring the amp back up, the tubes already have the B+ and this is where there is the issue

What is the value of the fuse? mA? Fast or slow blo?

Using the standby switch will pull much current. Because the two 100uf caps have low ESR they will pull a short but high load current. The 47uf caps will essentialy see a short circuit when the standby is turned on. Both the 47uf and 100uf caps will not be happy. Some hum when switching on is normal in the given schematic. I actualy think there is a mistake in the powersupply schematic. Either a part missing (Reactor coil) or the switch drawn in the wrong place. But this should not make your amp fail like it does.

Turning the amp on from standby, the power tubes will also pull high current for a moment. Could be there is a bad power tube that does not recover from this.

It is also important that the CF tube can take the high voltage (420 + 45 bias = way over the data sheet specs) The McIntoch amp this CF design was copied from used a Telefunken ECC83 tube. Both triodes will have close to 1mA plate current. Maybe try a different one. Sovtec tubes van take much abuse.

But first thing would be checking the value of the fuse.

Thanks for the help Richard

The mains fuse is 1.5A, 250V, slow blow. The HT is 500mA, slow blow

Do you have any suggestion on how to improve this standby? Attached the #121 power section, amp which uses the same SVT style power amp with the CF and the standby seems at the same place

I just bought a quad of TAD red plate. Maybe safe to wait for them before proceeding? I am concerned my power tubes may be gone. I may probably pull the CF out for the first trial with the new tubes. Any further suggestions?

My CF tube is a NOS Tungsram ECC83 (V46) Short Plates Halo Getter. I can try another one but probably with new power tubes?

Your HT fuse should be a higher value. Martin and I had a discussion about this, but I believe a 1A slow blo should be installed as HT fuse on the center ground tap.

Don't trow away your standby switch yet. Without center tap ground reference, strange voltages van occur. First replace the fuse and measure again.

I have ideas to improve the powersupply. In the schematic you posted there is a reactor after the standby. That's what i mean by a missing part in the 002. A remidy could also be changing the location of the switch.

[Bombacaototal]

1A, 250V, slow blow at the HT. Voltages check, all fine. Still have my CF tube out by the way but I have the two central power tubes

Stdby is still installed ,although non working

Should I try with a different ax7 tube at CF? I have TAD, GrooveTubes, RCA Blackplate. I am wondering if the low C- could have busted my previous one

EDIT: 4 power tubes in, without the CF. I turned on and off quickly a couple of times, does not seem to cause the hum issue. voltages in check

[martin manning]

Still have my CF tube out by the way but I have the two central power tubes...

EDIT: 4 power tubes in, without the CF. I turned on and off quickly a couple of times, does not seem to cause the hum issue. voltages in check

I've not been following closely, but the CF tube must be installed for the output tubes to bias correctly.

[Richard1001]

If anything, the low bias supply made things easyer for the CF tube. If it works leave it in there.

What is the type of switch you are using?

I once soldered a wire on a carling switch. I added solder and had to keep adding solder to make a good connection. I wondered where the solder went and found it was flowing down the heated solderlug into the switch. I turned the chassis around and heated the solderlug again. The solder came flowing back out. The switch is still working ..

I don't know what the problem is with your switches, but Maybe it helps.

[Richard1001]

Still have my CF tube out by the way but I have the two central power tubes...

EDIT: 4 power tubes in, without the CF. I turned on and off quickly a couple of times, does not seem to cause the hum issue. voltages in check

I've not been following closely, but the CF tube must be installed for the output tubes to bias correctly.

Yes, without the tube the bias voltage is 1/2 x the biassupply voltage. Close to - 175 V in this case.
This indeed will not hum or do anything, since the tubes are cut off by the low bias voltage

[Richard1001]

1A, 250V, slow blow at the HT. Voltages check, all fine. Still have my CF tube out by the way but I have the two central power tubes

Stdby is still installed ,although non working

Should I try with a different ax7 tube at CF? I have TAD, GrooveTubes, RCA Blackplate. I am wondering if the low C- could have busted my previous one

EDIT: 4 power tubes in, without the CF. I turned on and off quickly a couple of times, does not seem to cause the hum issue. voltages in check

Try the groove tubes. Is it the 12ax7-c? The older ones with square getter are very strong.

[rccolgan]

This is a weird one, Rafael!
I don't have any thoughts or suggestions at this point however I'll add some data points. Note: My bias is not the modified bias. I'm still using the parallel pot to adjust the resistance (see picture).

One of the SSS I built had the 10uF bias cap go bad. It did blow the HT fuse until it was replaced. This one went bad. https://www.mouser.com/ProductDetail/80-PEG124YF2100QL1

I did have the issue where the standby switch break a few times mechanically. I thought I over-torqued them when I installed but I think the arcing internally welded the leads shut. I now just use the typical SPST Fender switches which appear to handle the standby function a lot better than others.

[Richard1001]

Note: My bias is not the modified bias that Richard/Erwin came up with. I'm still using the parallel pot to adjust the resistance (see picture).

I don't use a bias pot in my 002 and did not come up with a modified bias control. It looks like Rafael is using the parallel bias pot.

If I had to come up with a bias control, i would put the variable resistor in the voltage devider that sets the bias voltage, not in the powersupply.

[Bombacaototal]

As far as the standby Switch:
- This was the first that failed: https://modulusamplification.com/Carlin ... 75378.aspx
- And subsequently this one two times, although the second it worked until I heard the loud hum and the HT fuse went down: https://www.mouser.co.uk/ProductDetail/ ... cycode=GBP

I have -364V on the C- without the CF tube (negative side of the bias cap and Bias called lug on the PI PCB), not half like Martin and Richard mentioned. B+ of CF on the PI PCB is 437V

The groovetubes is GT-ECC83-S

My bias cap that went bad is the same https://www.mouser.com/ProductDetail/80-PEG124YF2100QL1

I am using the parallel bias pot like Ryans layout

[Richard1001]

I have -364V on the C- without the CF tube, not half like Martin and Richard mentioned

The groovetubes is GT-ECC83-S

On the powertube grids the voltage is 1/2 the negative supply voltage without the CF tube installed.

[Bombacaototal]

Got it Richard, many thanks. So I added TAD to the CF. I have turned on with 4 power tubes and it was fine, off and on again, a bit of PT hum (zyeumm sound) for a few seconds then all fine. A slight pop when I turned off.

Quick recording. Amp was on at the beginning then I turn off. Then I turn on again and the last pop you hear is when I turn off. It has the TAD CF and the 4 power tubes. Standby is in the amp bit still the non working one

I think probably the original issue was the bias cap going bad, but after that was the low HT fuse. Probably both are fixed now. Thanks everyone for the help and support, that was a difficult one and I am relieved to have come through with your support

Just tried the old CF tube and it seems fine. Just a few outstanding questions, Should I replace the standby? Are there stil points of concern (maybe besides the standby)? Also why might mine and Ryans bias cap gone bad, manufacturing issue?