JM/Wonderland amp issues

[norburybrook]

My JM/Wonderland has been making some intermittent noises of late that have seemed to disappear after time but today they got worse from the get go. I noticed that when I hit a hard note all 4 6L6s would have a blue flash in the same top corner which coincided with the breakup/bad noise.


My thoughts were it can't be a tube as they all are doing exactly the same thing. I pulled 2 tubes to check and no difference. They've not had a lot of use anyway.

Does this mean my OT is on the way out? I used a donor amp for this build using 80s USA Peavey transformers.


M

[10thTx]

I'm wondering if that might be parasitic oscillation? Ironically, the only time I've had that happen was with an amp that had brand new tubes.

With respect, 10thtx

[xtian]

Blue flashes in tubes are not necessarily related to any fault condition. It's pretty common. Often you'll see power tubes flashing blue in amps like Princeton Reverb with bias-vary tremolo.

So, basic troubleshooting. Is it vibration related? Isolate the head from the cab to confirm.

[norburybrook]

Blue flashes in tubes are not necessarily related to any fault condition. It's pretty common. Often you'll see power tubes flashing blue in amps like Princeton Reverb with bias-vary tremolo.

So, basic troubleshooting. Is it vibration related? Isolate the head from the cab to confirm.

no it's not vibration related, hard strikes of the strings make a bad crackling sound in conjunction with the blue flashes at the base of the tubes.



M

[Colossal]

Tubes with soft vacuum will ionize to produce a lovely deep purple glow which is constant and maintained and can flutter in time with a trem, as Xtian says. "Flashing" on hard transients to me implies pending fireworks and something about to go...like a street car sparking down the street when it makes intermittent contact with the power line above. Which one is it, Marcus?

Edit: you were just posting as I was, Marcus. Oof...flashing at the base...that can't be good

[martin manning]

I agree all tubes behaving the same way strongly suggests the problem is elsewhere. Do the plate and screen voltages look good? Idle current still where it's supposed to be? Is this the one with the high plate voltage?

[norburybrook]

Tubes with soft vacuum will ionize to produce a lovely deep purple glow which is constant and maintained and can flutter in time with a trem, as Xtian says. "Flashing" on hard transients to me implies pending fireworks and something about to go...like a street car sparking down the street when it makes intermittent contact with the power line above. Which one is it, Marcus?

Edit: you were just posting as I was, Marcus. Oof...flashing at the base...that can't be good

Dave,

when I say the base I mean internally at the base, exactly the same point in each tube as if it's the same pin.

Doesn't look or sound normal to me, it was the sound that first drew my attention so I looked at the tubes when it was happening and saw these small flashes.

I'll open her up tomorrow....ah the joys of tube amps


M

[norburybrook]

I agree all tubes behaving the same way strongly suggests the problem is elsewhere. Do the plate and screen voltages look good? Idle current still where it's supposed to be? Is this the one with the high plate voltage?

yes it is martin from the peavey transformers, around 500v. SOunded great by the way

I'm off to bed now. got a plumber coming early in the morning to fit a new boiler..that blew up as well.....





M

[Colossal]

Marcus, the great thing about tube amps is that if one fails catastrophically, we can just build another And we are always looking for a reason to build just one more.

[norburybrook]

well..took it out of the cab today. Everything looked good inside. Spotted one solder joint on a heater that I thought could be better so re-flowed that. fired it up, perfect, no issues...ah lets less how it goes, I doubt it was the solder joint affecting all valves so who knows. I think the amp sounds a little noisier(hum) than I remember, perhaps it's because I've got it dimed anyway, great sounding amp with all the NFB off and dimed I did think about removing the cut control and putting the SSS filter on as the chassis is drilled for it would just need a new faceplate.

Anyone got any thoughts on this?



M

[Bombacaototal]

well..took it out of the cab today. Everything looked good inside. Spotted one solder joint on a heater that I thought could be better so re-flowed that. fired it up, perfect, no issues...ah lets less how it goes, I doubt it was the solder joint affecting all valves so who knows. I think the amp sounds a little noisier(hum) than I remember, perhaps it's because I've got it dimed anyway, great sounding amp with all the NFB off and dimed I did think about removing the cut control and putting the SSS filter on as the chassis is drilled for it would just need a new faceplate.

Anyone got any thoughts on this?



M

The 002/004 filters (I tried both) voice the amp to a more “nasal” sound, compared to the JM 1M/68K. I think the high filter only works well in the bypass and next two positions, after that the amp starts to sound a bit dull/compressed/constipated (I don’t like). The low filter is extremely subtle, you will only be able to hear its effect on a larger cabinet. You will beed the inductor which does tighten the bottom end nicely. I’d say is subtle but audible compared to it bypassed.

The Martin Manning filter may be an interesting option...I would try it instead on a next build

[martin manning]

Leave it on for a while (got your heat back yet?) and see if it acts up again. Thinking about the increasesd hum, are the power supply filters comfortably rated for the voltage you are running?

[Bombacaototal]

I think one thing to keep in mind is that the 004 has more gain than the mayer and also has a different voltage structure, which are higher than what you see on the ODS amps

To me one of the best things you can do is adding a GNFB switch (ON-ON or ON-OFF-ON) with the Dumble value too (you will need to convert the feedback reduction from 4ohms to 8ohms, so the resistor will not be 4.7K). What I did was 4.7k on 4 ohms and 8.2k on 4ohms (equals the 12k on 8ohms). I build 3 amps with this switch and I cannot recall a situation where the looser (bassier) Mayer PI sounded better.

[norburybrook]

Leave it on for a while (got your heat back yet?) and see if it acts up again. Thinking about the increasesd hum, are the power supply filters comfortably rated for the voltage you are running?

Martin,

look at them

500w caps.JPG

They were the most expensive caps I've ever bought.

@Ra[phael, thanks for the heads up, I've got the local and global negative feedback on switches, I usually have them off. I've got slightly more gain from the voltage divider too from stock and 500v on the plates. Having some finer control on the bottom end would be nice as it gets a bit boomy when turned up loud.

Do you need the inductor? and are the filters a simple drop into the circuit?


M

[Bombacaototal]

Marcus, it is very easy to drop it in. The Mayer topology is essentially the 004 minis filters, and some different LNFBs and values. So it makes sense having the filters in this circuit.

I tried my 002 and 004 filters with the inductor bypassed and it works fine. I preferred the sound with the inductor just because I felt it tightened the bottom nicely

I’ve done them connected to one another like Dumble but also used the terminal strip in 2 other occasions. The terminals made it easier for me but going straight looks nicer