LANEY GH100L (no output)

[retrorod]

Got a Laney GH100L head with 5881's installed. Amp powers on and 10 seconds or so after, I hear a click sound and the plate voltage goes down. When I engage the standby off, the plate voltage goes up to 465V, but I am getting no sound from the amp or inputs.

Any Ideas? I know some about tube amps and I am carefull...

...Thanks, Rod

[g1]

There is a turn on delay relay which is probably the click you are hearing. There shouldn't be plate voltage when on standby, maybe it's just a bit of voltage left in the caps. So after the click, and out of standby, you should have around 460V on the plates of the power tubes. You said you have this so you are good so far.
Do you get any sound if you plug a signal (or guitar) into the FX return? Can you run the fx send into another amp to see if there is signal coming out of FX send? Have you tried a patch cord between the FX send and return jacks?

laneygh100l.pdf

[Zouto]

That's a common issue with several Laneys,GH100L, VH100R, V50. Too much SMD stuff inside, absolutely unreliable amps.
http://music-electronics-forum.com/t16301/
Probleme mit Laney VC50 - HV bricht ein/Amp geht aus.
I got the same trouble on my VH100R for years and could not fix it, swapping relay, switching transistors etc.
Even the official Laney Service could not fix it, swapping the same stuff, plus some FX loop parts.
So I'll never buy a new Laney anymore.
Hope you'll find a solution
Zouto

[retrorod]

There is a turn on delay relay which is probably the click you are hearing. There shouldn't be plate voltage when on standby, maybe it's just a bit of voltage left in the caps. So after the click, and out of standby, you should have around 460V on the plates of the power tubes. You said you have this so you are good so far.
Do you get any sound if you plug a signal (or guitar) into the FX return? Can you run the fx send into another amp to see if there is signal coming out of FX send? Have you tried a patch cord between the FX send and return jacks?

[ATTACH]16163[/ATTACH]

Thanks! I have tried all of the above, after your suggestion(It dawned on me that I have read that before)....No sound yet. I was tapping on the Output tubes. Only sound out of one. Checked the preamp tube plate voltage and it is nonexistant. No high voltage (200V) or so to be found...!!??

[Chuck H]

If you have no voltage on any preamp tube plate (I'm including the PI tube), but you do have noise coming from a power tube then it's likely the 22k/25W resistor between P54 and P55 or a contact point P54 or P55. If you have Vp on the PI but not the tube behind it (circuit wise, not physically) then check R27. If that tube has voltage but not the one behind it check R17. If that tube has voltage but not the input tube check R8.

[retrorod]

Thanks Chuck! Yes, no voltage on the Phase Inverter tube either...SO, the first scenariono. Is 22K indeed a 25 W resistor?

[Jazz P Bass]

Yup.
22K, 25 watt resistor.

[Chuck H]

The resistor may be fine. IMHE with a resistor that size (and why should it be in that circuit?) it's just as likely to be a burned board trace or pad. Or, if that resistor is oversized because a smaller one was failing (shouldn't have) maybe it got hot and unsoldered itself?!? Point is, there's no good reason I can see for that resistor to be so large. The fact that it is may indicate that there are other problems with the circuit/construction/layout... So who knows what may have failed? But wherever the failure is, it's likely to be that resistor or something related to that resistors connection to the board/s.

[retrorod]

Okay, I see on the schematic the resistor and P54 and P55. However, I see no P54 or P55 on my circuit or a large 22K25W Res.
There is a large 10K(tank-type) mounted to the chassis near this area. The Techs at Laney are very fond of shrink tubing and silicone goop, so it takes some extra cleaning to get a reading in a lot of areas.
Possible that this amp has a 10K R instead of a 22K.? I see no other large resistors in the 25 watt range.
Also, no evidence of burning or previous work, so I will investigate further on this evening.

[retrorod]

A quick check of that large 10K is giving some bad readings. Later, after removing silicone globs,I will test it out of circuit.
??---Should I replace it with the 22K or another 10K, if it is bad?

[retrorod]

Another question! What would be a good(safe) bias setting for the Sovtek 6L6WGC tubes? They are currently drawing low to upper 40ma depending on the tube. Plate voltage is about 460V

[g1]

See note 3 on the first schematic. Originally there were two 10K 1W in series (R42 & R43) which are shown on the page 3 schematic. These have been upgraded to a single 22K 25W. If you have an older model, it may have the two 10K's. If so, I think replacing them with 10K 5W's should work. 25W here is definitely overkill.
40mA per tube for bias sounds fine to me, that would be 18W idle dissipation each.

[Zouto]

Bias-wise I usually go for 36 - 38mA per 5881, 17W dissipation, for 460V plate voltage.
Long tube life, no excessive heat on the PCBs, good sound.

[Jazz P Bass]

That 25 watt rating sure does seem like overkill
As an aside, the Laney LH50 uses one 10K 25 watt resistor.

[retrorod]

I have got sound again!
Thanks to everyone for the help and advice! The 10K/25watt 'tank res.' was in OL never-land! So I clipped it and installed 2 -10K FP 1Watters in the R42 and R43 position on the pcb (pre-issue change).
So far So good. Not sure what the longevity will be though! Apparently this area was an Achilles Heel in the design. It is interesting that Jazz P Bass says that the Laney LH50 uses a 10K/25W also.
The schematic for the GH100L clearly calls for a change to a 22K/25W Thats a large resistor!
This is "the best" electronics forum for info that I have come across.....thanks, Rod