1W JTM build

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Re: 1W JTM build

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geoff 1965 wrote:
Tue 06/22/21 9:02 am
what about the filtering between V1a and V1b anodes Jack,could that account for the difference?
Do you mean the preamp filter caps? They are coupled on the same B+3 node as the plate resistors of V1a+b
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Re: 1W JTM build

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geoff 1965 wrote:
Tue 06/22/21 9:02 am
what about the filtering between V1a and V1b anodes Jack,could that account for the difference?
That wouldn't be a factor, because the two anodes are connected together. Even if they weren't, it wouldn't explain this. DC current flowing into either section through the cathode resistor must equal the current flowing out of that section through the respective anode resistor. There's no other path for the current to take, unless it's also flowing through the grid circuit due to a gassy tube. If that was the case, both sections would show the same fundamental imbalance because they're in the same envelope - cathode current would be higher than anode current. Cathode current equals the sum of all the other currents out of the tube.

Jack
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Re: 1W JTM build

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Did some experimenting.. higher B+ wasn't any nicer, on the contrary... on various bias settings. Now I landed on 264R (390//820R) and I'm pretty satisfied.
The discrepancy on V1 anodes and cathodes is due to the different cathode resistors. V1a is 2k2 and V1b is 1k5. I tested by lowering the cathode resistor on V1a and the voltages on that half both dropped substantially. So that's off the table...
I'll post a clip ASAP, but the power went down in the area...just while I was soldering the speaker to the cable ☹
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Re: 1W JTM build

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Bieworm wrote:
Tue 06/22/21 2:27 pm
Did some experimenting.. higher B+ wasn't any nicer, on the contrary... on various bias settings. Now I landed on 264R (390//820R) and I'm pretty satisfied.
The discrepancy on V1 anodes and cathodes is due to the different cathode resistors. V1a is 2k2 and V1b is 1k5. I tested by lowering the cathode resistor on V1a and the voltages on that half both dropped substantially. So that's off the table...
I'll post a clip ASAP, but the power went down in the area...just while I was soldering the speaker to the cable ☹
That's all good news! The schematic I was working from shows the V1 cathode resistors both at 1.5K. Seems like you're about done, and I think your client will be very pleased. Just need to let Josh critique the sound!

Jack
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Re: 1W JTM build

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TriodeLuvr wrote:
Tue 06/22/21 2:50 pm
Bieworm wrote:
Tue 06/22/21 2:27 pm
Did some experimenting.. higher B+ wasn't any nicer, on the contrary... on various bias settings. Now I landed on 264R (390//820R) and I'm pretty satisfied.
The discrepancy on V1 anodes and cathodes is due to the different cathode resistors. V1a is 2k2 and V1b is 1k5. I tested by lowering the cathode resistor on V1a and the voltages on that half both dropped substantially. So that's off the table...
I'll post a clip ASAP, but the power went down in the area...just while I was soldering the speaker to the cable ☹
That's all good news! The schematic I was working from shows the V1 cathode resistors both at 1.5K. Seems like you're about done, and I think your client will be very pleased. Just need to let Josh critique the sound!

Jack
Maybe I will keep the soundclip for myself and spare me the critique 😁😁😁
Naaah.. I wouldn't dare 😀
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Re: 1W JTM build

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Re: 1W JTM build

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OMG!!! I feel so stupid!!! Moron!!!!
Listen: the amp has a 0.1W attenuator switch... I was trying to fix the sound the entire time on that stupid 0.1W position!!!
Listen to this dudes.. this is the 1W position:
https://www.dropbox.com/s/jqt0i2dgi7vtq ... 1.m4a?dl=0
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Re: 1W JTM build

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Yay!! hurray hurray

But it's too good to sell now!

Jack
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Re: 1W JTM build

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TriodeLuvr wrote:
Wed 06/23/21 2:14 pm
Yay!! hurray hurray

But it's too good to sell now!

Jack
Naah.. it's good..awesome in fact, but still ain't no Tremolo TMB Reverb!!!
God, I feel so stupid.. I was checking how terrible the 0.1W switch would sound, because that kind of attenuating is never good sounding.. and katchinggg.. loud!!!
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Re: 1W JTM build

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Much better!

There's still a touch of articulation missing in a couple guitar positions (0:51-1:06, 2:58-3:11 mostly). That could be the amp, the speaker, or the pickups. Whatever it is, you could try adjusting the tone knobs (just turn them, don't replace anything) to get a little more mids, maybe a tiny bit less highs.

Overall though, very nice.

Thanks,
Josh
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Re: 1W JTM build

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JMPGuitars wrote:
Thu 06/24/21 6:41 am
Much better!

There's still a touch of articulation missing in a couple guitar positions (0:51-1:06, 2:58-3:11 mostly). That could be the amp, the speaker, or the pickups. Whatever it is, you could try adjusting the tone knobs (just turn them, don't replace anything) to get a little more mids, maybe a tiny bit less highs.

Overall though, very nice.

Thanks,
Josh
You're right. As for tone settings they are : Bass 12 O' clock / mid 3'O clock / treble 12 O' clock
there's already a 50k pot for the mids, with a .01uf cap. Maybe I'd better change the 500pf treble cap back to 250pf? Change the slope resistor to lower value? There's 56k in there right now.
I don't think the speaker is the problem.. it's a V30, so the least that one lacks is mids :wink:
I'm going to put the GE 12AU7 back in.. it seemed to sound better than the Mullard. The cathode voltage went up 0.15V with the mullard, compared to the GE.
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Re: 1W JTM build

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Bieworm wrote:
Thu 06/24/21 7:02 am
You're right. As for tone settings they are : Bass 12 O' clock / mid 3'O clock / treble 12 O' clock
there's already a 50k pot for the mids, with a .01uf cap. Maybe I'd better change the 500pf treble cap back to 250pf? Change the slope resistor to lower value? There's 56k in there right now.
I don't think the speaker is the problem.. it's a V30, so the least that one lacks is mids :wink:
I'm going to put the GE 12AU7 back in.. it seemed to sound better than the Mullard. The cathode voltage went up 0.15V with the mullard, compared to the GE.
Maybe, or try a different speaker. There are certainly points that feel like there's too much highs, and that's common with the V30. Try one of your sacred speakers and see what the difference is before changing anything else.

Thanks,
Josh
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Re: 1W JTM build

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Josh.. the moments on the recording you refer to are the ones where I play the tele neck pickup.. those are muddier by nature.
Does that explain some?
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Re: 1W JTM build

Post by JMPGuitars »

Bieworm wrote:
Thu 06/24/21 10:14 am
Josh.. the moments on the recording you refer to are the ones where I play the tele neck pickup.. those are muddier by nature.
Does that explain some?
Yes, I'm aware you switched the pickup. The question is- does that pickup normally sound muddy, or do you get better articulation in that position on other amps?
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Re: 1W JTM build

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JMPGuitars wrote:
Thu 06/24/21 11:35 am
Bieworm wrote:
Thu 06/24/21 10:14 am
Josh.. the moments on the recording you refer to are the ones where I play the tele neck pickup.. those are muddier by nature.
Does that explain some?
Yes, I'm aware you switched the pickup. The question is- does that pickup normally sound muddy, or do you get better articulation in that position on other amps?
I'll do a recording with my jazzmaster or the red tele I built. They are clearer in the neck pos.
I did the previous recording with the White tele. That one is blackguard voiced , muddy neck.
Just had rehearshal with the band for the first time since september.. 36W tremolo tmb reverb.. oh man this was awesome!!!
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