Spencerleehorton
Well-known member
I’ll change the 12ax7 tubes first before I start taking things apart.
Last edited:
JTM45 Build with 6P3P output tubes and GZ34
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Spencerleehorton
Well-known member
Took all tubes out apart from GZ34 and checked voltages, B+ 460v.
Turned on standby and dropped a bit to 457v.
Then put OT in and 12ax7s.
Power on B+ 460v as soon as standby turned on B+ drops to 403v!!
Bias was set at 43ma.
I then dropped bias to 36ma (el34)
This then put B+ to 414v from 403v
Checked out other voltages across the tubes and although they looked low it all looked consistent.
I wonder whether the GZ34 is damaged?
Turned on standby and dropped a bit to 457v.
Then put OT in and 12ax7s.
Power on B+ 460v as soon as standby turned on B+ drops to 403v!!
Bias was set at 43ma.
I then dropped bias to 36ma (el34)
This then put B+ to 414v from 403v
Checked out other voltages across the tubes and although they looked low it all looked consistent.
I wonder whether the GZ34 is damaged?
Spencerleehorton
Well-known member
I think what I will try is to revert back to the original way that B+ was connected and see if it is the same.
Spencerleehorton
Well-known member
Yep same problem, choke is fine so it must be gz34, so I’ve ordered a new one.
Accelerator
Well-known member
@Spencerleehorton
Man, ride out this shitty Radial 100 watt Output transformer and put in a proper & correct Output transformer for the tubes that you would like to use and at least use a matched pair of Output tubes …If you would like to use a matched pair of EL34 / KT77 / 6CA7 Output Tubes, you have to install a Drake type JTM50 3200 ~ 3600 (A-A*) 50 watt Output transformer and you will have nearly 50 watt output…
If you would like to use a matched pair of KT66 Output Tubes, you will have to install a Radiospades type JTM45 8000 (A-A*) 35 watt Output transformer and you will have nearly 35 watt output…
The whole “Spartan spirit” of the Marshall 35watt JTM45 amp. it is NOT for you to makes this Grande cheapie B.S. with this Shitty & Uncorrected Radial 100 watt Output transformer in this amp., and then to add the one B.S. after the other B.S., like the idiotic dangerous & cheapie B.S. with the 6P3P output tubes, then the B.S. with the P.PI.M.V. to tame down your higher wattage that comes from your Shitty & Uncorrected Radial 100 watt Output transformer with your unmatched pair of your EL34 tube, and then the B.S. with the Dual bias to matched your unmatched pair of your EL34 Output tubes, and then the B.S. with the Fx loop and the list of your B.S. goes on and on and on, asking continues like an attention slut for someone to helps you or to save you from your continues and dangerous B.S.…
Before you make any another new B.S. and asking continues like an attention slut for someone to help you from your continues and dangerous B.S. make yourself a favor to educate yourself by spending a little bit of your time to read this book:
Designing Tube Preamps for Guitar and Bass, 2nd edition by Merlin Blencowe
I don’t care, I don’t give a F*kk and I don’t have any economical or any other effort if you buy this book, if you download this book by a “pirate” site, if you read it in your public library, if you steal it from a book shelf or whatever else…
You MUST READ THIS BOOK because ‘till this time you are an Uneducated and Dangerous Newbie for yourself and for everybody near you and for the whole DIY-er Community…
By the way, like any Marshall amp. lover here & out there I have to tell you, that the Marshall 35watt JTM45 amp., it is not a “polymorphic” B.S. amp. like any “Mesa Boogie”-like amp., with all of these “add ons” and “add ons” and “add ons” to mods and mods and mods to ruin the whole sound…
The “Marshall Roar” sound it is like a malt whisky that you drinking it straight, you don’t ruin it…
Spencerleehorton
Well-known member
I’m going to ignore most of that as this is a learning exercise for me and may, I hope, help anyone else who may have similar issues.
I have reverted to the tube town schematic and redone the wiring as per that.
Still getting the drop from 465v on B+ to about 414v when standby is turned on but will change the GZ34 and see if improves.
Have also reverted to one bias pot and getting 37ma on each OT, just wanted to see if the bias wiring was the problem.
Will take out the third extra 10k on the last node of B+ and see if any change.
Mains txf does only seem to get a little warm now but only tested for about 20-30 minutes.
I have reverted to the tube town schematic and redone the wiring as per that.
Still getting the drop from 465v on B+ to about 414v when standby is turned on but will change the GZ34 and see if improves.
Have also reverted to one bias pot and getting 37ma on each OT, just wanted to see if the bias wiring was the problem.
Will take out the third extra 10k on the last node of B+ and see if any change.
Mains txf does only seem to get a little warm now but only tested for about 20-30 minutes.
If people weren't interested in helping you with your build they wouldn't comment 187 times on this thread. Don't be discouraged by Accelerator's attacking language.
Running mismatched tubes is not a problem, just not ideal.
Mismatched OT can work
Effects loop is ok if that's what you like - Marshall does it
Master volume is fine if that's what you like - Marshall does it (very common mod on vintage amps)
Building an amp with different output tubes is fine - Everyone does it
The trick is to know the changes you need to make to make it work, and that's what we're working toward. You might not get the classic Marshall tone with your combo, but it's not anyone else' amp but yours.
Cutting down on mismatches and parts that we're unfamiliar with would help troubleshooting and cut down on variables, but if the OTX and PTX are known to be good and you have datasheets for them, the problems are all solvable.
The valve wizard website is great source.
Built my first jtm45/100 off of info from uncle Doug, valve wizard, el34 forum and the Marshall plexi forum
That voltage drop seems fine, and wouldn't be a problem for the right transformer. You can calculate exactly how much current is getting pulled across the mains transformer with the voltage drop and your last filter resistor before the output transformer. This would tell you if you're in spec and you can look elsewhere for problems and not have to replace a gz34. GZ34 drops voltage on its own. There are charts for this on the web.
You're obviously not uneducated or dangerous - the amp sounds good and the guts look good. Troubleshooting is hard, especially when you're learning.
I think it would be most helpful here to do what you're doing and stick with one schematic and modify it one step at a time. Maybe it's time for a post to refresh everybody here on what exactly we're working on, and what the current problems are that you're trying to resolve, with up-to-date schematics.
Once it's working like the schemo, then we can better help you with mods
Running mismatched tubes is not a problem, just not ideal.
Mismatched OT can work
Effects loop is ok if that's what you like - Marshall does it
Master volume is fine if that's what you like - Marshall does it (very common mod on vintage amps)
Building an amp with different output tubes is fine - Everyone does it
The trick is to know the changes you need to make to make it work, and that's what we're working toward. You might not get the classic Marshall tone with your combo, but it's not anyone else' amp but yours.
Cutting down on mismatches and parts that we're unfamiliar with would help troubleshooting and cut down on variables, but if the OTX and PTX are known to be good and you have datasheets for them, the problems are all solvable.
The valve wizard website is great source.
Built my first jtm45/100 off of info from uncle Doug, valve wizard, el34 forum and the Marshall plexi forum
That voltage drop seems fine, and wouldn't be a problem for the right transformer. You can calculate exactly how much current is getting pulled across the mains transformer with the voltage drop and your last filter resistor before the output transformer. This would tell you if you're in spec and you can look elsewhere for problems and not have to replace a gz34. GZ34 drops voltage on its own. There are charts for this on the web.
You're obviously not uneducated or dangerous - the amp sounds good and the guts look good. Troubleshooting is hard, especially when you're learning.
I think it would be most helpful here to do what you're doing and stick with one schematic and modify it one step at a time. Maybe it's time for a post to refresh everybody here on what exactly we're working on, and what the current problems are that you're trying to resolve, with up-to-date schematics.
Once it's working like the schemo, then we can better help you with mods
Spencerleehorton
Well-known member
I’m now using the tube town schematic, I have changed the wiring of the B+ as per the schematic minus the 48k resistor across the standby switch.
The 2 x 100R I have left off the GZ34.
Mains txf tests as 2 x 337 / 336vac
, 6.18vac on heaters and 4.88vac on heater of GZ34.
B+ is 465v
Standby switch is 414v
8.2k = 317v
10k = 250v
10k = 220v
Mains transformer get to about 40C after about 30 minutes then I turn off as I get volume drops.
Michael at modulus amplification who made the mains transformer, choke and I do have a output transformer from him but he has said not to use it with EL34 due to him using smaller gauge wire so he could fit all the winds on there.
But has said I can send the transformer back and he will test and send me another one.
I have tested without tubes and just gz34 and voltages all look normal.
Then added back in OT and tested again and still get drop to 414v once standby is turned on.
I have ordered another GZ34 to see how voltages look and good to have a back up anyways.
I might take out the gz34 and put in some diodes which will put me at about 475v after the bridge rectifier and then test again.
Maybe an option to have this switched. The benefit would be if in the future the GZ34 had any problems I can just switch to solid state.
The 2 x 100R I have left off the GZ34.
Mains txf tests as 2 x 337 / 336vac
, 6.18vac on heaters and 4.88vac on heater of GZ34.
B+ is 465v
Standby switch is 414v
8.2k = 317v
10k = 250v
10k = 220v
Mains transformer get to about 40C after about 30 minutes then I turn off as I get volume drops.
Michael at modulus amplification who made the mains transformer, choke and I do have a output transformer from him but he has said not to use it with EL34 due to him using smaller gauge wire so he could fit all the winds on there.
But has said I can send the transformer back and he will test and send me another one.
I have tested without tubes and just gz34 and voltages all look normal.
Then added back in OT and tested again and still get drop to 414v once standby is turned on.
I have ordered another GZ34 to see how voltages look and good to have a back up anyways.
I might take out the gz34 and put in some diodes which will put me at about 475v after the bridge rectifier and then test again.
Maybe an option to have this switched. The benefit would be if in the future the GZ34 had any problems I can just switch to solid state.
Well, I can't even chalk your devastating language to you not being a native English speaker. You have enough command of it to be perfectly heard.
Your words are deliberately rude and insulting, and clearly infringing rule #4.
https://groupdiy.com/threads/groupdiy-rules-read-before-posting-in-any-of-the-forums.6650/
Although not specifically addressed in the group's rules, improper language is not encouraged (euphemism). If you think this helps you to carry your message, think twice, it does not make you look good.
I don't think it's a good idea to use power transformer bolts for ground connections, esp. the safety ground (which should be on its own and not shared with anything else). Might want to check out this thread:
https://ampgarage.com/forum/viewtopic.php?f=9&t=37456
re: the weird harmonizer stuff, it's generally referred to as "ghosting" and can have various causes such as the guitar, speaker(s), and (maybe the more obvious?) residual B+ ripple modulating the signal plus lack of hum cancellation (I guess this is "common mode rejection"?) of the push-pull output. Some people think it's cool if at a small degree, but for others it drives them crazy. Check out a couple of these threads:
https://ampgarage.com/forum/viewtopic.php?t=32742
https://ampgarage.com/forum/viewtopic.php?f=9&t=31923&start=45
(After reading through the 13 page "JTM45 rectifier question" thread (phew), I think one of the problems was a build (implementation) issue (maybe more than one), where the wire carrying AC to the bias circuit is twisted together with a B+ line wire going to a filter/de-coupling cap (which is part of the signal loop).
In that amp garage thread the ghosting issue was resolved by adding another stage of filtering (which would obviously reduce ripple), but someone asks the question (on page 9 of the thread), "Why is such extreme filtering required to make this amp behave when a 5F6-A, essentially the same circuit, works fine at 450V using Rectifier-40uF(plates)-4H-20uF(screens) ??", so I tend to think the implementation was not quite up to par.
I remember a very old thread years ago on ampage (BBS), where someone with a (model) 1962 "Bluesbreaker" (basically the same thing as JTM45 but a combo which includes tremolo) was having issues after having the amp retrogressed to the more early vintage circuit (which has less filtering--the reiss. had all 50uFs). One of the things mentioned which apparently improved on the ghosting was shielding the AC carrying wire going to the bias circuit (the chassis is wider in the Bluesbreaker and that wire is run a long way along the back panel then up toward the PCB).
To me, the Fender 5F6-A bias circuit (for that AC wire) looks better than the Marshall JTM45 (one part where they deviated a little bit from the Fender layout) since it's further away from other stuff and short.
https://ampgarage.com/forum/viewtopic.php?f=9&t=37456
re: the weird harmonizer stuff, it's generally referred to as "ghosting" and can have various causes such as the guitar, speaker(s), and (maybe the more obvious?) residual B+ ripple modulating the signal plus lack of hum cancellation (I guess this is "common mode rejection"?) of the push-pull output. Some people think it's cool if at a small degree, but for others it drives them crazy. Check out a couple of these threads:
https://ampgarage.com/forum/viewtopic.php?t=32742
https://ampgarage.com/forum/viewtopic.php?f=9&t=31923&start=45
(After reading through the 13 page "JTM45 rectifier question" thread (phew), I think one of the problems was a build (implementation) issue (maybe more than one), where the wire carrying AC to the bias circuit is twisted together with a B+ line wire going to a filter/de-coupling cap (which is part of the signal loop).
In that amp garage thread the ghosting issue was resolved by adding another stage of filtering (which would obviously reduce ripple), but someone asks the question (on page 9 of the thread), "Why is such extreme filtering required to make this amp behave when a 5F6-A, essentially the same circuit, works fine at 450V using Rectifier-40uF(plates)-4H-20uF(screens) ??", so I tend to think the implementation was not quite up to par.
I remember a very old thread years ago on ampage (BBS), where someone with a (model) 1962 "Bluesbreaker" (basically the same thing as JTM45 but a combo which includes tremolo) was having issues after having the amp retrogressed to the more early vintage circuit (which has less filtering--the reiss. had all 50uFs). One of the things mentioned which apparently improved on the ghosting was shielding the AC carrying wire going to the bias circuit (the chassis is wider in the Bluesbreaker and that wire is run a long way along the back panel then up toward the PCB).
To me, the Fender 5F6-A bias circuit (for that AC wire) looks better than the Marshall JTM45 (one part where they deviated a little bit from the Fender layout) since it's further away from other stuff and short.
