Any #124 clips around?

[Mark]

I must admit that I am curious on your mod ands results.

[odourboy]

FWIW, I did a scratch build on a Ceriatone chassis and faceplates. The chassis is a bit flimsy and I had to mod it to accommodate the iron I used (Bassman stuff from Allen), but overall it was successful.

Brian,

Did you use a 340v-0-340v TP40 model? If so, do you remember the dropping string and voltages? I have one of those PTs waiting to be put into service. Sorry for the derail.... KILLER CLIPS Gil!

Thanks,
Dave

Yep - that's the PT I used. The high voltage coming off it is on the high side (487 VDC @ 122VAC mains). Here's the string I ended up with:

470R 5W (WW) RF mod in place of choke
5K 5W (WW)
18K 2W
2K7 2W
120K 2W FET board simulator

B+1 ~487V
B+2 ~477V
B+3 ~424V
B+4 ~320V
B+5 ~309V

YMMV - I've come to learn over time that there's a significant variation in current draw from one 12AX7 to the next, which will impact your plate voltage and the B+ voltages, all else being the same. IMHO, this is one reason why tube swapping can have such an impact on the amp's tone.

B.

[ayan]

YMMV - I've come to learn over time that there's a significant variation in current draw from one 12AX7 to the next, which will impact your plate voltage and the B+ voltages, all else being the same. IMHO, this is one reason why tube swapping can have such an impact on the amp's tone.

B.

Well I'll be damned, I had never thought about the effects of tube swaping from that standpoint, but it sounds like curent draw could certainly be a factor.

Cheers,

Gil

[lunastromoner]

Huh, I never thought about that... Is there a simple way to test 12AX7's for current draw?

So if Nik isn't making the chassis anymore (I emailed him but he hasn't responded yet), what do people use? I've seen the Natchanis chassis, but I would rather not have "Dumble" all over the chassis... Is there anyone who makes chassis or should I get a bare one and start drilling?

[stelligan]

Yep - that's the PT I used. The high voltage coming off it is on the high side (487 VDC @ 122VAC mains). Here's the string I ended up with:

470R 5W (WW) RF mod in place of choke
5K 5W (WW)
18K 2W
2K7 2W
120K 2W FET board simulator

B+1 ~487V
B+2 ~477V
B+3 ~424V
B+4 ~320V
B+5 ~309V

YMMV - I've come to learn over time that there's a significant variation in current draw from one 12AX7 to the next, which will impact your plate voltage and the B+ voltages, all else being the same. IMHO, this is one reason why tube swapping can have such an impact on the amp's tone.

B.

Thanks Brian.
And yep. I discovered the current draw thing in a rather brash sounding D'Lite build I had. In my limited swapping, I found it interesting that a certain JJ drew the voltages down about 9 volts lower and tamed that amp nicely. The JJ's I tried consistently drew more current than the EH's I had on hand. Has anyone done any extensive testing of this? Derail #2 - sorry.....

[talbany]

Gil

You posted this on the gear page I believe.. Are you using 250K OD Level on your amps? Curious!!

as opposed to 124 which is a Skyliner with 100K plate load resistors and a couple of tweaks. The specific tweaks were: larger pre OD entrance trimmer -- 350K VS 100K -- and larger than usual "Level" post (250K VS the usual 100K). Both of those changes will contribute to make the overdrive in the amp sound darker and muddier. However, note that the 100K plate load resistors will make the overdrive brighter and harsher right out of the gate, so maybe with new caps and tubes the amp would sound balanced. To me, as already stated, it was more an amp for a Keith Richards kind of sound, with the capability of a liquid overdrive for good measure.

Tony VVT

[Mark]

I'm not sure current draw is the correct term, I'm thinking the whole current draw thing is more or less the gain of a particular tube. While the gain of a 12AX7 is quoted as being 100, in reality the gain of a 12AX7 must fall within a certain range.

That is the way I see it. If I'm incorrect please explain why I am incorrect.

Of course the experiment to do now is to replace the cathode resistors with a 2K linear pot in series with a 1K resistor and adjust each tube you put into the amp for the same current draw and plate voltage and see what they sound like. Maybe there are people blowing a lot of cash on NOS tubes when a $2 pot would solve their woes.

Regarding the above mentioned experiment. I think there possibly would be no audible difference in tone at all, of course I could be wrong.

[ayan]

Gil

You posted this on the gear page I believe.. Are you using 250K OD Level on your amps? Curious!!

as opposed to 124 which is a Skyliner with 100K plate load resistors and a couple of tweaks. The specific tweaks were: larger pre OD entrance trimmer -- 350K VS 100K -- and larger than usual "Level" post (250K VS the usual 100K). Both of those changes will contribute to make the overdrive in the amp sound darker and muddier. However, note that the 100K plate load resistors will make the overdrive brighter and harsher right out of the gate, so maybe with new caps and tubes the amp would sound balanced. To me, as already stated, it was more an amp for a Keith Richards kind of sound, with the capability of a liquid overdrive for good measure.

Tony VVT

No, I use a 100KL level pot, and my pre OD network is 220K + 100K trimmer.

Gil

[talbany]

No, I use a 100KL level pot, and my pre OD network is 220K + 100K trimmer.

Gill

Thanks Bro!!


Tony

[ayan]

No, I use a 100KL level pot, and my pre OD network is 220K + 100K trimmer.

Gill

Thanks Bro!!


Tony

Remember I do use my ultra secret, patented treble gate at the input of the "Ratio" (lead master) control (= .001uF cap + 250K variable resistor to ground, set about halfway up). I use a 150K resistor at the output of V2B, and without the treble gate thing, the amp (with 100K plate load resistors) will be too bright in overdrive mode reagrdless of just about anything else -- and if you don't hear it that way, you're deaf.

Gil

[Zippy]

Yep - that's the PT I used. The high voltage coming off it is on the high side (487 VDC @ 122VAC mains). Here's the string I ended up with:

470R 5W (WW) RF mod in place of choke
5K 5W (WW)
18K 2W
2K7 2W
120K 2W FET board simulator

B+1 ~487V
B+2 ~477V
B+3 ~424V
B+4 ~320V
B+5 ~309V

YMMV - I've come to learn over time that there's a significant variation in current draw from one 12AX7 to the next, which will impact your plate voltage and the B+ voltages, all else being the same. IMHO, this is one reason why tube swapping can have such an impact on the amp's tone.

B.

Thanks Brian.
And yep. I discovered the current draw thing in a rather brash sounding D'Lite build I had. In my limited swapping, I found it interesting that a certain JJ drew the voltages down about 9 volts lower and tamed that amp nicely. The JJ's I tried consistently drew more current than the EH's I had on hand. Has anyone done any extensive testing of this? Derail #2 - sorry.....

It's a good derail. How 'bout measuring the plate voltage on V1 instead of focusing on the dropping string? As you've both noted, it's the voltage on the tube that matters. What is the voltage when it sounds good?

[stelligan]

Thanks Brian.
And yep. I discovered the current draw thing in a rather brash sounding D'Lite build I had. In my limited swapping, I found it interesting that a certain JJ drew the voltages down about 9 volts lower and tamed that amp nicely. The JJ's I tried consistently drew more current than the EH's I had on hand. Has anyone done any extensive testing of this? Derail #2 - sorry.....

It's a good derail. How 'bout measuring the plate voltage on V1 instead of focusing on the dropping string? As you've both noted, it's the voltage on the tube that matters. What is the voltage when it sounds good?

Zippy,
On the build I was referring to - I was focusing on the preamp tube plates. I had been swapping OD 12ax7 tubes. EH I had in V2 was giving 212v on V2a and 219v on V2b. The JJ I ended up with brought V2a to 203v which sounded real good to me. It was a Bassman PT "D'Lite" HRM with 220k/150k on V1, 180k/150k on V2 . Voltages on V1(a & b) were: 190v & 196v. I haven't messed with tubes and trimmer since and am very happy with that amp. Anyone with absolutely ideal voltage values for V1 & V2? I'll search some more.



Thanks,
Dave

[odourboy]

Can't say that these are 'ideal' but I like to shoot for 188-195V range on V1 and maybe 195-202V range on V2.

[talbany]

Remember I do use my ultra secret, patented treble gate at the input of the "Ratio" (lead master) control (= .001uF cap + 250K variable resistor to ground, set about halfway up). I use a 150K resistor at the output of V2B, and without the treble gate thing, the amp (with 100K plate load resistors) will be too bright in overdrive mode reagrdless of just about anything else -- and if you don't hear it that way, you're deaf. Very Happy

Gill

Just trying to figure out why 124 was a 100k plate amp and didn't use your ultra patented super secret treble bleeder circuit...LOL!! and from what you described the OD in 124 wasn't bright or brittle in any way...Or maybe it was and I just missed that one.... If I did I apologize!!.. I wonder if this wasn't the reason why he used a 350K OD entrance and 250K Ratio?...It may be that your amps voltages are about 30v higher on the plates as well..w/ New Sensor Transformers as we all know what 30 more volts can do...I am not a big fan of the 100k plates I prefuer the 180/150.......180/120 and 250K Od entrance and 250k Ratio and when I went up on the values of these 2 pots I noticed a much more tame high end in this topology... No big deal just scratching my head here!!!


Tony VVT

[jelle]

JJ's short plate 12ax7's draw more current...yes Mark, current draw is the correct term here, just measure across the plate resistors and you'll see, so the JJ will drop the voltage a bit more.

Not a bad tube either, IMHO.

Jelle