Two days off so I built this

[randalp3000]

Been super busy so no amp time until last Saturday. Thought this thing up last winter and got burned out. I wanted to try something lower voltage/higher current with 6L6, 6V6, or 6K6's and my favorite preamp. It took me 2 1/2 days to get it punched and wired. Only problem was I wired the heaters for the power tubes to pin 6 instead of 7 .

[David Root]

Why the .022uF on the non-entrance side? Was this a tweak after startup or did you plan it that way?

Other than that the PI is a 2nd/3rd generation Dumble ODS with less balanced plates (82K/100K vs. 100/110).

This value would only partially bypass that side and result in a perceived treble boost. Compared with the usual 0.1uF in that position.

[randalp3000]

Why the .022uF on the non-entrance side? Was this a tweak after startup or did you plan it that way?

Other than that the PI is a stock 2nd/3rd generation Dumble ODS.

This value would only partially bypass that side and result in a perceived treble boost. Compared with the usual 0.1uF in that position.

I actually built it with .05 uF and will update the schematic when I get some more time. The cathode resistor I used is a 150R and I'm getting around 80mA on each 6L6 with a plate voltage around 300v.

Finally got to play it for about ten minutes. Very responsive and not stupid loud when cranked. Lots of clarity with good note separation. So far quite fun little amp.

[randalp3000]

Here it is so far.

[rp]

What are the 2M2Rs on the switch for, prevent popping? Did it work? I was looking at the output taps, is that a Tweed Bandmaster OT?

[M Fowler]

2m2 resistors are to prevent pops from discharging caps.

That is a Magnetic Components 40-18088 40 watt 6k OT the same one I use for my Express combo amps.

[rp]

Every time I put a resistor across a switch to prevent a cap popping it never worked I think I've used 10M.

That's the Tweed Super & BM OT. So you've used that in an Express? 6V6s or EL34s? Guess it worked well or you would have yanked it. I would have thought it was too primitive a wind and maybe too dirty for an Express. For no good reason I figured it was a bigger 5E3 OT, but maybe only because it has no shrouds.

[gktamps]

Thanks for posting this.

How does that 6k OT work with 6K6GT tubes? I have wanted to build an amp with 6K6 tubes for awhile, but thought they worked best with about double that impedance?

Cheers,

Greg

[pdf64]

Why the .022uF on the non-entrance side? Was this a tweak after startup or did you plan it that way?
...
This value would only partially bypass that side and result in a perceived treble boost. Compared with the usual 0.1uF in that position.

Why should that be so?
How much attenuation at 82Hz results from a 22nF bypass cap on the LTP non-inverting input (compared to 0.1uF)?

[M Fowler]

Every time I put a resistor across a switch to prevent a cap popping it never worked I think I've used 10M.

That's the Tweed Super & BM OT. So you've used that in an Express? 6V6s or EL34s? Guess it worked well or you would have yanked it. I would have thought it was too primitive a wind and maybe too dirty for an Express. For no good reason I figured it was a bigger 5E3 OT, but maybe only because it has no shrouds.

Sorry Randal for treading on your thread.

Here are my Two Express combo amps using this 6k OT with EL34's.

https://tubeamparchive.com/viewtopic.php?t=7911 Sound tracks on page 4 of this thread.

https://tubeamparchive.com/viewtopic.ph ... highlight=

[rp]

MF I remember reading that post, guess I over looked the OT. Funny, no questions/comments to you or the OP here on the OT choice, people will do the lazy loop with the exact loops, use the same silicone as KF for the stack o'caps, but no one asked about the deviant use of a BM OT? Much less headroom, earlier break-up?

I'm not on Facebook, but I doubt you'd be using it if it didn't sounds good.

Maybe you both should have a 3x10 cab built for the next one, never played a tweed BM but people claim there's a unique magic about them.

[M Fowler]

It sounds just like my other Express heads, loud and aggressive.

[randalp3000]

how much current can 6L6's handle? can I run them at 100% like cathode biased EL84's? right now I think I'm at around 80% but want to kick it up.

thanks
rp

[rp]

It's my understanding you can run a cathode biased amp 100% with no trouble, as it self regulates. I run mine that way, I never like the sound when the Rk gets too far from spec (in a clone anyway) but I'm not a gigging musician and I don't care if I run tubes hard. I would just do it, check them in the dark for red spots and blast away. If it blows up you get to rebuild it! BTW I don't think it'll be noticeably louder, that whole power to db logarithmic thing.

[randalp3000]

updated schematic