#183 revisited (mods to my liking)

[markusw]

Hi Electron,

thanks for the gut shots!
What's that trimmer on the relay board for?

Regards,

Markus

[hans-jörg]

Hi,
Whats the effect of the cap and R in front of the 220k OD entrance and why not on an 100k anode amp?

Btw.: whats the effect on an 100k anode amp (124 low plate) when I put a (f.e. ) 250p parallel with the 220k entrance resistor?

Best

Hans-Jörg

PS: nice and interesting build "electron"!

[hans-jörg]

Again one of Gil's gems: Treble Cut mod: 0.002uF cap with 250k trimmer after 180k resistor going to OD Volume (Ratio).

This really brought the amp to new life. Now I can use the Neck PU of my Tele without synth like bass string OD. The bridge PU still has plenty of meat. A Strat sounds very nice as well, as do Humbuckers in a Love Rock Tokai.

Hi @marcusw,

I guess its this one.
I have it in mine too (124 low plate) but with 1n and a 500k trim. switchable. Nice tool.

Hans-Jörg

[markusw]

Hi Hans-Jörg,

Btw.: whats the effect on an 100k anode amp (124 low plate) when I put a (f.e. ) 250p parallel with the 220k entrance resistor?

The 250p will enhance the treble. If I'm correct, the knee (-3db) of the high pass filter can be calculated from the value of the cap (i.e. 250p) and the value of the OD trim pot. 6366 Hz for 250p and 100k OD trim, 2546 Hz for 250p and 250k OD trim.

I guess its this one.
I have it in mine too (124 low plate) but with 1n and a 500k trim. switchable. Nice tool.

I guess the treble bleed might be the small perf board with trimmer and cap close to the OD output.

Peace,

Markus

[hans-jörg]

Hi Hans-Jörg,

Btw.: whats the effect on an 100k anode amp (124 low plate) when I put a (f.e. ) 250p parallel with the 220k entrance resistor?

The 250p will enhance the treble. If I'm correct, the knee (-3db) of the high pass filter can be calculated from the value of the cap (i.e. 250p) and the value of the OD trim pot. 6366 Hz for 250p and 100k OD trim, 2546 Hz for 250p and 250k OD trim.

I guess its this one.
I have it in mine too (124 low plate) but with 1n and a 500k trim. switchable. Nice tool.

I guess the treble bleed might be the small perf board with trimmer and cap close to the OD output.

Peace,

Markus

Thank you Markus.

So I have there a 500k Pot - so the 250p lost his elegibility

Yes, the small board is the treble bleed.

Best

Hans-Jörg

[markusw]

Thank you Markus.

So I have there a 500k Pot - so the 250p lost his elegibility

Yes, the small board is the treble bleed.

Best

Hans-Jörg

With 500k it would be roughly 1270 Hz. You could of course use just a e.g. 120p for ~2500 Hz.

Peace,

Markus

[hans-jörg]

This is all a misunderstanding from my side. I have done everything to eleminate fizzy highs in OD (treble bleed, etc.) but on the entrance I feed the highs. Terrible.

Nice weekend
Hans-Jörg

[markusw]

Have a "leiwand" weekend too

Regards,

Markus

[dogears]

I have two amps with variations of the 183 circuit. Neither of them has any of the traits you describe.

As such, I'd suggest two things.

Tubes
Speaker

I run my 2X12 G1265 cab and it is really sweet with this circuit.

Also, tubes matter. Currently I like the old brown base Tesla EL34 in there. Preamps tubes matter too! Maybe try some Holland made Amperex. These are warm and fat. No fizz. What are you running??

Lastly, setting the pre-od trimmer too high has bad effects on the bass (as you noted?). Try no more than 22K-23K or so and the bass cleans up nice. In my experience. This is another reason why NOS tubes work well in this circuit. The bottom handles the bass better.

Thanks!

[ElectronAvalanche]

Hi Scott, Hans-Jörg, Markus,

the trimmer on the PAB relay board is the variation of the PAB: simply lifiting the Tonestack, but with a variable resistor to ground (=trimmer, 250k). Since I never was happy with the original Dumble PAB I used this PAB scheme in the amp as shown.

The small board next to the OD output is indeed the Ayan Treble bleed (or shall we say Dumble inspired Ayan Treble / HF trim?).

@Scott:

I followed your suggestions and reduced the PI output caps to 0.05uF (from 0.1uF) and installed some EL34 (only a pair since my PT is from a Fender Twin, thus the heater current capacity is for 4x6L6 only). Although this gave me a nice upper mid character, the bass was still there, thus prompting me to use the Ayan OD input bass trim trick.

The OD had quite a bit of high treble so I installed a 250k OD input trim before using the HF trim, but replaced that again with 100k, since the 250k gave me too much bass again.

So now I have the trimmer (100k) set to 23k and I like the sound quite a bit. I tested the amp with a Strat and the neck pickup is a bit too bassy, but that is how Strats are. With the bridge PU of the Strat or even better with my Tele on bridge the sound is quite nice now.

I plan on doing some clips but am in the middle of moving, so this might take some time.

I currently use a homebrew 1x12 ported cab (Dumble plans) and have a EV12L in there. Might get the chance to get some G1265 (15Ohms) for a 2x12 or my 4x12. Or I might build another 1x12 using a Fane Studio 12L.

Of course NOS power tubes might be the trick. I have some GE 6L6GC (clear dome) and a pair of Sylvania 6L6GC and maybe try them, but these tubes have some milage on them.

Currently I have TAD 6L6GC STR as output and some Telefunken ECC83 (long plate) in OD, EH in PI and EH in Clean (V1). I know about the short plate GE 12AX7 and wonder if there is a modern equivalent (sort of).

I try to stick with modern tubes and tweak the circuit to taste, since NOS is IMHO just too expensive for an amp that might see some serious gigging....

Thanks again for all the input!

Cheers,

Electron

[dogears]

Interesting.... I find this circuit to be nicer with the EL34. I have a 50 watt amp that I tried it with. I wound up modifying the NFB on it. Try more power amp feedback to tighten the bottom. With the 2 EL34s installed. Maybe start with the 4.7K on the 8 ohm tap. I liked a 5.1K on the 8 ohm on the 50 watter.

Bass cleaned up and the amp sounds spectacular.

In 100 watt mode, you would not typically do this. However, 6L6 tubes have much more bottom, especially the TAD. Adjustments may be in order. Such as V1B feedback?

Let us know!

[ampdork]

Haven't read the whole thread. If it's a bass issue with 6l6 I agree with Scott with v1b nfb... imho that is a must....mileage varies.

[ElectronAvalanche]

Hi Scott and Ampdork,

thanks for the info.

I have the NFBL as a switch on the amp, so I can choose between 22M, 44M and non.

For cleans I really like no NFBL. With the Strat the OD is best with 44M.

The TAD tubes might be very bass heavy. Any recommendation for other tubes? I have the Tungsol 6L6 reissue in my other amp and might try them.

I have a set of 7581 from GT but one tube seems to go out of spec, having a significantly higher current.

The OT is from a Fender PA (Twin iron) having 4 Ohms, my FBL has 4k7 from 4 Ohms. I had 6k8 there before with the HRM and that was nice as well. But I think the 4k7 is ok for now.

Cheers,

Electron

[dogears]

I was saying to try the 2 EL34 tubes. Try a 3.3 or 3.9 resistor. It totally worked on my 50 with the 183 circuit!

Hi Scott and Ampdork,

thanks for the info.

I have the NFBL as a switch on the amp, so I can choose between 22M, 44M and non.

For cleans I really like no NFBL. With the Strat the OD is best with 44M.

The TAD tubes might be very bass heavy. Any recommendation for other tubes? I have the Tungsol 6L6 reissue in my other amp and might try them.

I have a set of 7581 from GT but one tube seems to go out of spec, having a significantly higher current.

The OT is from a Fender PA (Twin iron) having 4 Ohms, my FBL has 4k7 from 4 Ohms. I had 6k8 there before with the HRM and that was nice as well. But I think the 4k7 is ok for now.

Cheers,

Electron

[stelligan]

Haven't read the whole thread. If it's a bass issue with 6l6 I agree with Scott with v1b nfb... imho that is a must....mileage varies.

Works for me. I had a switch there, and promptly removed it to LNFB always on.