Into the rabbit hole...36 Watt EL34 Superlite TMB

Double-Bubble! Place for discussing the 36W version...

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Billy_Goat
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Re: Into the rabbit hole...36 Watt EL34 Superlite TMB

Post by Billy_Goat »

Powered up my build today following Rob Robinette's DIY startup procedures.

All was going well until I added in the two V1 & V2 12AX7's at which time I detected the faint smell of something getting ready to smoke. All readings on my AC current and voltage meters were looking ok, but I visually could see ( and smell ) that the 1.5k 5W resistor between the two 50uF can caps was blackening to the point where the resistor code bands made the resistor appear like it was a 10R resistor instead of the required 1.5k resistor that I'm sure I wired in. My thermal temperature reader was showing this resistor sitting a bit under 200F.

So, I powered down, and removed the burnt resistor - which incidentally still read 1.5k - and replaced with a new 1.5k 5W resistor. Not seeing anything amiss after repeated previous highlighter run throughs and again another now, I crossed my fingers and tried again.

After an hour, all seemed well and the resistor was reading about 80F. Not sure what was going here, but...

Anyway, after adding in the power tubes, I let the amp cook for another hour and then pulled the tests voltage attached here. Everything seems to check out with a few over & unders by 10%-ish or less. ( Josh, I'm aware you have another thread in this forum where you want folks to post their voltage readings for this build which I will do when the build is completed.... ).

Please let me know if anyone sees any issues that I need to address here regarding voltages.

Didn't have time to move on to audio / signal testing, so that's next up... fingers crossed...

I do have one question... are there any particular tests / measurements I should make to confirm the correct operation of the FX send & return section other than simply plugging in a pedal or two and testing that way?

Cheers!
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Re: Into the rabbit hole...36 Watt EL34 Superlite TMB

Post by Billy_Goat »

Followup up to the above...

After running the amp with both signal and guitar, all seems well with the exception of the FX circuit.

Volume is bold, loud and clear. Gain control working. Fat / Bright switch working as I would expect. All tone controls working. Amp sounds amazing!

As for the FX circuit... if I plug a straight guitar cable ( no pedals or effects ) between the send and receive jacks, there's no affect on the amp in general. When plugging in a pedal ( tried a delay and then tried a reverb pedal ), there's a horrid high frequency screaming noise (oscillation?). Inadequate shielding?

So, I'll go back and recheck the connections for the FX circuit, but any input anyone could add here for how to troubleshoot would be appreciated. Josh previously indicated earlier in this thread that this part of the circuit can be prone to stability issues, so maybe even a re-think of how I now have this area wired / shielded?

Thanks in advance!

Cheers!
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Re: Into the rabbit hole...36 Watt EL34 Superlite TMB

Post by JMPGuitars »

Your voltages look great! I'm looking forward to hearing a sample of your amp.

Post some photos of your FX loop from a couple different angles so we can see what's going on. The solution could be as simple as chopsticking the leads to avoid the oscillation.

Thanks,
Josh
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Re: Into the rabbit hole...36 Watt EL34 Superlite TMB

Post by ViperDoc »

Did you go with the 36 watt GDS transformer set on these amps or another make?
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Billy_Goat
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Re: Into the rabbit hole...36 Watt EL34 Superlite TMB

Post by Billy_Goat »

ViperDoc wrote:
Tue 02/16/21 11:51 pm
Did you go with the 36 watt GDS transformer set on these amps or another make?
Yes, along with a GDS JTM chassis that I retrofitted for this build.

Cheers!
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Re: Into the rabbit hole...36 Watt EL34 Superlite TMB

Post by JMPGuitars »

Billy_Goat wrote:
Wed 02/17/21 9:54 am
ViperDoc wrote:
Tue 02/16/21 11:51 pm
Did you go with the 36 watt GDS transformer set on these amps or another make?
Yes, along with a GDS JTM chassis that I retrofitted for this build.

Cheers!
Post some photos, that sounds cool.
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Re: Into the rabbit hole...36 Watt EL34 Superlite TMB

Post by ViperDoc »

I'm sure that's an awesome chassis. I modded a Valvestorm 18-watt chassis for my Superlite build and it was a killer deal.

https://valvestorm.com/Products/MetroAmp
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Re: Into the rabbit hole...36 Watt EL34 Superlite TMB

Post by Billy_Goat »

JMPGuitars wrote:
Tue 02/16/21 9:26 am
Your voltages look great! I'm looking forward to hearing a sample of your amp.

Post some photos of your FX loop from a couple different angles so we can see what's going on. The solution could be as simple as chopsticking the leads to avoid the oscillation.

Thanks,
Josh
FX circuit issue resolved!!!

After careful reanalysis and studying of the schematic, it became clear that I had miss wired the jacks. D’oh!

After a quick re-wire and testing, all is well. Yay!!! Effects are clean and as clear as a bell.

I do have an unrelated question about the schematic vs the build doc... The schematic shows the pilot light being fed power from the 6.3v heater secondaries, where the build doc shows the pilot lamp being fed using the 5v secondary. I’m guessing either way works without any issues, but curious if this just an over sight between the two documents or just an inconsequential second path option? I ended up wiring my pilot using the 5v secondary in hopes of extending the life of the pilot lamp with a little less voltage.

As for the chassis, I retro fitted an already in hand combo cabinet and speaker setup that is loaded with a Reeves Vintage Purple 12”speaker. This is supposedly a close recreation of early 1970’s era Fane speakers. This speaker sounds very nice. Very punchy and ballsy with a nice bottom end thump. I alternatively tried a Scumback 65W M75-PVC that also sounded ok, but was a bit more ‘fizzy’ and not quite as punchy. The Scumback sounds amazing in my 18W build, though. Curious to know what speakers other folks with 36W builds are choosing?

As for sound clips, not sure how to make that happen atm as my shelter-in-place COVID home is many miles away from my recording and other studio gear and not easily accessible for now. Not sure that a recording using a phone would be the best means of showing off the build.

Anyway... pictures will follow as it’s now a bit too dark here now to take good photos.

Cheers!
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Re: Into the rabbit hole...36 Watt EL34 Superlite TMB

Post by JMPGuitars »

Well done!

The pilot thing was basically laziness. It doesn't really matter where you connect it between the two choices, but the unused rectifier heater tap is kinda better since it's not doing anything else.

My favorite speaker right now is the WGS BlackHawk (50W). Sounds great on 18W and 36W builds.

Thanks,
Josh
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Re: Into the rabbit hole...36 Watt EL34 Superlite TMB

Post by ViperDoc »

If you feel the urge, the Fane A60/F70 combo is absolute dynamite when broken in with the Superlite TMB. OMG.
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Re: Into the rabbit hole...36 Watt EL34 Superlite TMB

Post by JMPGuitars »

ViperDoc wrote:
Thu 02/18/21 11:35 am
If you feel the urge, the Fane A60/F70 combo is absolute dynamite when broken in with the Superlite TMB. OMG.
Post a demo. I wanna hear them! ;)
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Re: Into the rabbit hole...36 Watt EL34 Superlite TMB

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Picture of the internal wiring...
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Re: Into the rabbit hole...36 Watt EL34 Superlite TMB

Post by Billy_Goat »

Control panel... a retro fit into an already in hand cabinet...
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Re: Into the rabbit hole...36 Watt EL34 Superlite TMB

Post by JMPGuitars »

Very nice! Overall it looks like some really nice, clean work. I can't wait to hear it. ;)
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Re: Into the rabbit hole...36 Watt EL34 Superlite TMB

Post by ViperDoc »

Billy_Goat wrote:
Thu 02/18/21 3:32 pm
Picture of the internal wiring...
WHITE LOOP JACKS. (searching the internet...) 8)
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Re: Into the rabbit hole...36 Watt EL34 Superlite TMB

Post by TriodeLuvr »

ViperDoc wrote:
Thu 02/18/21 11:52 pm
Billy_Goat wrote:
Thu 02/18/21 3:32 pm
Picture of the internal wiring...
WHITE LOOP JACKS. (searching the internet...) 8)
That's a really clean build! I think AES has the white Cliff jacks.

Jack
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Re: Into the rabbit hole...36 Watt EL34 Superlite TMB

Post by Billy_Goat »

ViperDoc wrote:
Thu 02/18/21 11:52 pm
Billy_Goat wrote:
Thu 02/18/21 3:32 pm
Picture of the internal wiring...
WHITE LOOP JACKS. (searching the internet...) 8)
1/4" Jack - Cliff, White, Solder Lug
https://www.amplifiedparts.com/products ... solder-lug
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Re: Into the rabbit hole...36 Watt EL34 Superlite TMB

Post by JMPGuitars »

CLIFF also makes different color nuts for those jacks. I know newark.com can get them, I assume some other suppliers as well.
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Re: Into the rabbit hole...36 Watt EL34 Superlite TMB

Post by ViperDoc »

Thanks for the link. I wonder if they make a white vintage version with the metal ferrule, but with a white bezel. I prefer those jacks to the plastic nuts. I seem to strip those too easily.

EDIT: Well what do you know?

https://www.newark.com/cliff-electronic ... Connectors
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Re: Into the rabbit hole...36 Watt EL34 Superlite TMB

Post by Billy_Goat »

After a fair bit of playing and fussing with effects in the FX loop, it appears that the FX loop on my build is exhibiting a bit of comb filtering and / or phasing shifting that is manifesting as a slight unpleasant ‘hollow’ sound overall compared to when I play without using the FX loop. Not sure how to further confirm this and / or how I would go about trying to rectify if in fact more than just my impression? Any thoughts?
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