martin manning wrote: ↑Mon Dec 16, 2019 8:07 pm
That is quite a large miss match, and probably the source of the hum. Try swapping the output tubes side to side and see if the idle current miss match follows the tubes or the stays with the socket. If the hot bias stays with the socket, you may be leaking HV DC somewhere.
For separate bias you can parallel another pot and tail resistor. That means drawing a bit more bias current, but it’s only a few mA. You may have to decrease the upstream resistor to get back to the same bias voltage range.
Idle power tube bias is static (zero signal) balance, and the PI trimmer is dynamic (with signal) balance.
Thanks Martin. If I was leaking HV DC would it be in the PI section? if so I've replaced that whole section with #124 values so it's possible I might have a poor joint as getting stuff out and then in again is tricky.
I measured either side of the screen resistors and they were 447v DC on both tubes and the bias was -42v coming in on both tubes.
norburybrook wrote: ↑Mon Dec 16, 2019 11:10 pmI measured either side of the screen resistors and they were 447v DC on both tubes and the bias was -42v coming in on both tubes.
Sounds like the tubes are indeed miss matched. When you said you got that from two different sets I had to wonder.
put a brand new set of Tube town 6L6s in and they bias at 40.03 and 40.01 mA don't think you'd ever get any closer could actually be too close for maximum harmonic content.....
Anyway that's it. Calling it done.
50w #124 low plate skyliner combo , with 100k OD entrance trim, switchable FET boost, on board Dumbleator, 9v pedal power from footswitch and Celestion Classic lead 80
thanks for everyone's help, once again learned a lot from this build.
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over and out
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So, 18 pages of tweaking and trouble shooting further, you ended up with a almost stock #124? That, I think, is funny my friend and much like my tweaking end in many cases. Did a JTM50 once and converted it to a 2204 jcm800/1987 and later to a Bogner extacy blue channel, only to convert everything back years later and be happy again with the amp. So maybe I should change my name to Tweakz and you to Tweakburybrook.
Now, how much do you like the amp? Where did you set the trimmer? What guitars and speakers do you like with it?
In contrast to what I’ve read many times here, I still like my humbucker guitars more on my little #124 more than my strat.
Bombacaototal wrote: ↑Tue Dec 17, 2019 2:31 pm
Looks stunning. Why did you decide to goop it Marcus?
first reason was because I'd made so many changes on a tight ,cramped board it looked a bit shabby and I also had to raise the trim pot above other components as there was no room. Remember I had originally designed and built this as a second gen so no trim pot, so the distance between components was too narrow to sit the pot down.
Secondly I knew it would stop me tweaking once it was gooped
rootz wrote: ↑Tue Dec 17, 2019 7:00 pm
So, 18 pages of tweaking and trouble shooting further, you ended up with a almost stock #124? That, I think, is funny my friend and much like my tweaking end in many cases. Did a JTM50 once and converted it to a 2204 jcm800/1987 and later to a Bogner extacy blue channel, only to convert everything back years later and be happy again with the amp. So maybe I should change my name to Tweakz and you to Tweakburybrook.
Now, how much do you like the amp? Where did you set the trimmer? What guitars and speakers do you like with it?
In contrast to what I’ve read many times here, I still like my humbucker guitars more on my little #124 more than my strat.
yes, I built another combo a few years ago and did exactly the same thing, came back to standard BM form after trying a lot of tweaks
Trimmer is set at about 30k from ground. Guitars? I mainly use telecasters of various kinds, standard, P90, filtertrons.
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The speaker is a Celestion Classic Lead 80, I had one I could use from another cab otherwise I might have gone with a Celestion Alnico Cream. I had originally used the Neo B12 300N but wasn't quite sure about the OD tone.
@Erwin
I'll try do a clip if I get time before christmas, just finished my touring and now have to do my Tax return before Christmas and a few other bit's and pieces before i go away for a well earned break. Hopefully when I return i will be booked into Hospital to have my heart re booted
M
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because we can ....another Low plate? that's an assumption they're Charlies NOS Dales
I've one Chassis left now. I shall be having a good think what to build as my last build. The 6G6-B is calling me at the moment, with perhaps a wreck/Komet type bass channel I'm also thinking of dusting off the JTM again to see how that's fairing, might do a couple of mod's with the NFB to switch between fender and Marshall values. I'm also interested in trying a 2x10 of somekind to go with the 6G6 maybe or the JTM. i saw Greg Koch recently and hi 2x10 combo in a small club sounded amazing...really amazing....changed my view on 10's
because we can ....another Low plate? that's an assumption they're Charlies NOS Dales
I've one Chassis left now. I shall be having a good think what to build as my last build. The 6G6-B is calling me at the moment, with perhaps a wreck/Komet type bass channel I'm also thinking of dusting off the JTM again to see how that's fairing, might do a couple of mod's with the NFB to switch between fender and Marshall values. I'm also interested in trying a 2x10 of some kind to go with the 6G6 maybe or the JTM. i saw Greg Koch recently and hi 2x10 combo in a small club sounded amazing...really amazing....changed my view on 10's
M
Went back and forth on this one and finally settled on a low plate classic w/Deep config this time round. This will more than likely be my last build for quite some time as I am now totally out of CTS pots and my last stash of seasoned iron. Might as well go ahead and clear them all out on this build. The collection will finally be complete accept for a 124. I do have a quad of perfectly matched RCA Black plates so I am looking forward to putting those to good use in a D-Style amp. If it turns out half way decent I may do a combo w/ EVL (Back breaker) We'll see. If I were to build another amp it would be another JTM 45. Slowly collecting all the parts now.
I am a big fan of the 10's The clip I posted a while back on the Music Man was my 4X10 Marshall closed back w/35w White labels.(sounds real close to the old 65's) great sounding cab and light too.
BTW. The NFB switch on a JTM sounds good.
Tony
" The psychics on my bench is the same as Dumble'"
because we can ....another Low plate? that's an assumption they're Charlies NOS Dales
I've one Chassis left now. I shall be having a good think what to build as my last build. The 6G6-B is calling me at the moment, with perhaps a wreck/Komet type bass channel I'm also thinking of dusting off the JTM again to see how that's fairing, might do a couple of mod's with the NFB to switch between fender and Marshall values. I'm also interested in trying a 2x10 of some kind to go with the 6G6 maybe or the JTM. i saw Greg Koch recently and hi 2x10 combo in a small club sounded amazing...really amazing....changed my view on 10's
M
Went back and forth on this one and finally settled on a low plate classic w/Deep config this time round. This will more than likely be my last build for quite some time as I am now totally out of CTS pots and my last stash of seasoned iron. Might as well go ahead and clear them all out on this build. The collection will finally be complete accept for a 124. I do have a quad of perfectly matched RCA Black plates so I am looking forward to putting those to good use in a D-Style amp. If it turns out half way decent I may do a combo w/ EVL (Back breaker) We'll see. If I were to build another amp it would be another JTM 45. Slowly collecting all the parts now.
I am a big fan of the 10's The clip I posted a while back on the Music Man was my 4X10 Marshall closed back w/35w White labels.(sounds real close to the old 65's) great sounding cab and light too.
BTW. The NFB switch on a JTM sounds good.
Tony
Tony, if you look in the last pic of the post above you'll see my closed back Marshall 4x10 cab with Celestion G10's under the JTM 45 with KT 66's . I'm going to fit a line out on it so I can try wet/dry , it's become my favourite way of adding reverb/delay and I like having the level on a volume pedal too, very flexible way of dialling in your verb/delay levels dynamically........
, great minds
I still have a vintage EVM12 sat unused here.
@Jeff (10thTX) I'll look into this
...right back to my tax return...I'm procrastinating here.......
don't think you'd ever get any closer 
