18 watt Superlite TMB Reverb

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TriodeLuvr
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Re: 18 watt Superlite TMB Reverb

Post by TriodeLuvr »

Bieworm wrote:
Sat 07/10/21 3:48 am
Just looked for those types, but it's nog going to be easy to find them here.
Actually, I'm kinda biased towards the 12AU7 in the previous build. I was very impressed. Might go the double 12AU7 PP in parallel route...
OTOH a pentode would offer some other options like G2 control and stuff...
Dilemma's... but it's a september build, so there is time
The 12AU7 in parallel mode will double the output power to roughly 2 or 2.5W. That's a 3dB increase, barely discernible to the ear. The following will do better than that, nearer the top of the output range you mentioned. Do any of these tubes show up on eBay over there? I know they won't necessarily be found at guitar parts retailers.

(One) 6BL7
(One) 6BX7
(Pr) 12B4
(Pr) 6AK6
(Pr) 5686 (in triode mode)
(Pr) 6AH4GT
(Pr) 12BY7 (in triode mode)
(Pr) 6CL6 (in triode mode)
(Pr) 6197 (in triode mode)

You could also use a pair of somewhat larger pentodes in triode mode, maybe the 6AQ5, but with reduced B+ supply voltage for earlier saturation. Not quite the same effect as clipping at the grid, so this might affect the overdrive tone.

Jack
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Re: 18 watt Superlite TMB Reverb

Post by Bieworm »

TriodeLuvr wrote:
Sat 07/10/21 1:33 pm
Bieworm wrote:
Sat 07/10/21 3:48 am
Just looked for those types, but it's nog going to be easy to find them here.
Actually, I'm kinda biased towards the 12AU7 in the previous build. I was very impressed. Might go the double 12AU7 PP in parallel route...
OTOH a pentode would offer some other options like G2 control and stuff...
Dilemma's... but it's a september build, so there is time
The 12AU7 in parallel mode will double the output power to roughly 2 or 2.5W. That's a 3dB increase, barely discernible to the ear. The following will do better than that, nearer the top of the output range you mentioned. Do any of these tubes show up on eBay over there? I know they won't necessarily be found at guitar parts retailers.

(One) 6BL7
(One) 6BX7
(Pr) 12B4
(Pr) 6AK6
(Pr) 5686 (in triode mode)
(Pr) 6AH4GT
(Pr) 12BY7 (in triode mode)
(Pr) 6CL6 (in triode mode)
(Pr) 6197 (in triode mode)

You could also use a pair of somewhat larger pentodes in triode mode, maybe the 6AQ5, but with reduced B+ supply voltage for earlier saturation. Not quite the same effect as clipping at the grid, so this might affect the overdrive tone.

Jack
The ones I can get here is:

6BX7GT ratheon at 22€/pc NOS

Worth a try ? It's SE then? Is the 125A OT a good match?

The only good shop for NOS tubes is this one that sells jukebox parts:
https://www.jukebox-revival.eu/catalogs ... t/?q=+6bx7
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Re: 18 watt Superlite TMB Reverb

Post by TriodeLuvr »

Just for background, the 6BX7 and it's cousin, the 6BL7, have gained favor over the last few years for some hi-fi applications. The 6BX7 exhibits a somewhat lower anode resistance, so it's a favorite in certain applications where that's perceived to be an advantage. Because of this, the 6BX7 often sells for twice as much, even though the difference is really not very significant. I'm only mentioning this because the 6BL7 might be less expensive, if you can find it.

These tubes can be used single-ended, with both sections in parallel, or in push-pull, just like you used the 12AU7. Maximum anode dissipation with both sections operating is 12W, VS 5.5W for the 12AU7. It's a really tough tube, and it can be pushed. Note that filament current is 1.5A. This creates a large electron cloud within the tube that makes it capable of significant peak current capability. That translates to what I call "attack dynamics."

Incidentally, you wouldn't be the first to do this. There used to be a Web page describing a guitar amp that a guy built using a 6SN7 dual triode, similar to the power level of a 12AU7. I think it was push-pull, but not certain now. Anyway, he said the difference when he switched to the 6BX7 was huge, almost too much volume to still be considered a low-power amp.

I wish that page was still up, it would save some time. The main difference is the higher B+ that can be used (VS the 12AU7), and the output transformer needs to be around 6K or 8K, plate to plate. For single-ended, 5K is appropriate, but output power would be considerably less than AB1 push-pull. I believe the push-pull version with one tube can output three to four watts.

Jack
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Re: 18 watt Superlite TMB Reverb

Post by TriodeLuvr »

Here's a link to a couple 6BX7 hi-fi amps. The second one uses a single tube in push-pull. This circuit uses an 8K transformer, and it's a pretty good model of how to build the power amp stage. I would probably use a somewhat higher B+, but it's not critical.

https://www.bonavolta.ch/hobby/en/audio/6bx7.htm

EDIT: Here's a guy who loves tubes almost as much as I do! Note the list on the left also shows the 6BX7.

http://vinylsavor.blogspot.com/search/label/6BL7

Incidentally, if you go SE instead of PP, the 6CK4 is another option. It's a single octal triode rated 12W. Of coursed, there's always the EL84 in triode if you do that, and it draws a lot less filament current. Overall, I think building another amp like the 12AU7 - but with a 6BL7/6BX7 - is the way to go. You've aready got everything else dialed in.

Jack
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Re: 18 watt Superlite TMB Reverb

Post by Bieworm »

Thanks Jack. That's something to really consider on doing
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Re: 18 watt Superlite TMB Reverb

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I just acquired a Vox Escort 50 Bass combo for 100€. It's a ragged old amp, which is very nicely aged and an inspiration for relic guys.
The size and look of the cab is what made me buy it. I've always had a weak spot for voxes, just for the looks of them.
Now I've got some decisions to make, but I'm leaning towards making a JTM 45 out of it.
Later on I'm going to open her up and see if there are parts to reassign besides the speaker.
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Re: 18 watt Superlite TMB Reverb

Post by TriodeLuvr »

I'd be tempted to convert that to something like a VOX AC30. Just to keep it in the family. :)

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Re: 18 watt Superlite TMB Reverb

Post by Bieworm »

TriodeLuvr wrote:
Wed 07/14/21 11:27 am
I'd be tempted to convert that to something like a VOX AC30. Just to keep it in the family. :)

Jack
Naaahh.. on 2nd thought..it's a better candidate for my low watter tremolo tmb. It's 10cm lower and 5cm narrower than my 18 watts.
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Re: 18 watt Superlite TMB Reverb

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Ok... it's started. Chassis drilled.. ready for wiring the heaters. Turretboard drilled too
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Re: 18 watt Superlite TMB Reverb

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Some more progress. This will be it for another week.. I'm off to France tonight.
Power supply is almost ready...
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Re: 18 watt Superlite TMB Reverb

Post by Bieworm »

Ok. Power supply finished. B+ line too. And input jack wired until the grid of V1a.
VoCom G2 controller is preparated and will be connected/tested AFTER the amp is up and running to spec.
Edit: had to redo some wiring in the B+ line. Stupid mistake...
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Re: 18 watt Superlite TMB Reverb

Post by Bieworm »

Mark foil side of the caps
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Re: 18 watt Superlite TMB Reverb

Post by JMPGuitars »

Bieworm wrote:
Mon 07/26/21 1:15 pm
Mark foil side of the caps
20210726_200841.jpg
You so fancy!
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Re: 18 watt Superlite TMB Reverb

Post by Bieworm »

Aaahhhh shame! On holiday again til Sunday, and that's how I have to leave the build behind. Only the PI wiring to be finished and the power tube wiring to be done...
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Re: 18 watt Superlite TMB Reverb

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Finished wiring the amp yesterday. After all checks I fired her up and all things are fine. No noises or issues at all, and sounds healthy and fine.
Voltage after rectification is too high, as I expected. 372VDC. I added 2x 6V zeners and that brought the B+ back to 362VDC. Still too high. Today I will knock that down.
I have a discrepancy in the plate voltages of the PI that need some attention. I didn't wrote the grid and cathode voltages down, but they're fine.
I also put in a 2.2uf cathode bypass cap for the fat switch. The 1uf wasn't fat enough, but it's part of the fine tuning process...we'll see.
Reverb voltages are lower than the tremolo TMB reverb. The B+ dropping resistors aren't the same values for that matter, so that explains. But the verb's nevertheless nicely sounding.
So after I get the B+ to spec I will be making the connections of the G2 controller. I'm very curious how that will behave..
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Re: 18 watt Superlite TMB Reverb

Post by JMPGuitars »

Bieworm wrote:
Mon 08/02/21 12:10 am
I have a discrepancy in the plate voltages of the PI that need some attention.
That plate voltage discrepancy doesn't matter. That's a very small margin.

After you get your B+ voltage to the sweet spot, you might want to adjust the reverb voltage, but if it sounds good, it's obviously optional.

Thanks,
Josh
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Re: 18 watt Superlite TMB Reverb

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Got the voltages where they should be, more or less... for now I will settle for that.
The G2 controller works, but it's not that linear as I would expect. When you turn it more down it drops, but rises back immediatly. Not to full power, but still. When you roll it down to 9 O'clock it's clearly less in volume, but overdrives more than it was set to on the gain. I think it works, but one needs to learn to use it I guess...
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Re: 18 watt Superlite TMB Reverb

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Combo almost ready. White piping still to do, along with the handle and rubber feet.
The guy wants tilt back legs!!! Dank, only Fender sells such things... would break my heart to add those 🙄
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Re: 18 watt Superlite TMB Reverb

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Assembled...
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Re: 18 watt Superlite TMB Reverb

Post by JMPGuitars »

Very nice! Though I'm sure you already know my next question... ;)
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