Hi All
Building 2 JTM 45 right now, I want to ask away
I use Gold Lion Tube depot tubes. Anyway I got "38" bias point.
With a 220K drop resistor and the 68K flying resistor at idle the bias is 1.5 amps over the recommended 38 and that's with the pot fully cold. I would like to have the pot in the middle point to have more control over the BIAS range.
I tried a 150 K drop resistor, got me there (lower) but the bias was only 33 mA I ran a ****** OT and the plate reads 465 VDC
I don't have a 180K to try, I wanted to know if I increased the flying resistors value to 75K or 82K would that get me where I need to be?
I see all the original schematics and they say 150K drop and 56K flying.
The kit calls for 68k / 220k
What would be my next logical step
Thanks in advance
Dan
JTM 45 Bias question
Moderator: VelvetGeorge
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JTM 45 Bias question
MetroAmp addict!
JTM 50/45,1987's & 1986
1959 and 2203/2204 Amps
1974 amp
Can't stop building, very addictive!
JTM 50/45,1987's & 1986
1959 and 2203/2204 Amps
1974 amp
Can't stop building, very addictive!
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Re: JTM 45 Bias question
Try 82. Use whatever value gives you the sweep you want. Yes, change the flying resistor that is attached to the bias pot.
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Re: JTM 45 Bias question
Ok Thank You I was thinking this after I posted however wanted to confirm
Thanks for your insights
Regards
Dan
Thanks for your insights
Regards
Dan
MetroAmp addict!
JTM 50/45,1987's & 1986
1959 and 2203/2204 Amps
1974 amp
Can't stop building, very addictive!
JTM 50/45,1987's & 1986
1959 and 2203/2204 Amps
1974 amp
Can't stop building, very addictive!
-
- New Member
- Posts: 37
- Joined: Fri Dec 19, 2014 11:34 am
- Just the numbers in order: 13492
Re: JTM 45 Bias question
I got it addressed. What I did, I ordered two 38 hardness sets from TD and anyway here's what happened
I put in set A and v4 was 36 ma and v5 was 39-40. What a shitty match set. So before swapping the flying resistor I took out set A and installed set B. Let the amp warm up for 30 minutes on max cold bias. Checked the plates and they were 455 VDC. I got similar numbers to set A and then split the sets. I took the pair that were 36 and put them in and now the amp is at 65-70% and the pot is at 1/3 travel.
Not too happy about the tubes. Maybe their machines aren't accurate or better yet maybe the operator made a mistake.
Anyways the "hot set" will go in the other amp I'm building "it's replacement" as I built the other one for a customer and I think I'll have to up the flying resistor to 82k to get it where it should be
Thanks for the replies
Regards
Dan
I put in set A and v4 was 36 ma and v5 was 39-40. What a shitty match set. So before swapping the flying resistor I took out set A and installed set B. Let the amp warm up for 30 minutes on max cold bias. Checked the plates and they were 455 VDC. I got similar numbers to set A and then split the sets. I took the pair that were 36 and put them in and now the amp is at 65-70% and the pot is at 1/3 travel.
Not too happy about the tubes. Maybe their machines aren't accurate or better yet maybe the operator made a mistake.
Anyways the "hot set" will go in the other amp I'm building "it's replacement" as I built the other one for a customer and I think I'll have to up the flying resistor to 82k to get it where it should be
Thanks for the replies
Regards
Dan
MetroAmp addict!
JTM 50/45,1987's & 1986
1959 and 2203/2204 Amps
1974 amp
Can't stop building, very addictive!
JTM 50/45,1987's & 1986
1959 and 2203/2204 Amps
1974 amp
Can't stop building, very addictive!