High Voltage Hijinks

[Hal Harvey]

THERES JUST TOO MANY THINGS TO DO AND KIDS TO FEED. PRIORITIES MAN PRIORITIES!

Btw, all didn’t go well this time. Had some problems during a test play. Clean sound was amazing, but when driven with square wave not so. Overall volume was also reduced and rising preamp gain caused outputs partial/total cutoff and crackling note decay.

Schematic here, red marks most recent changes. It’s missing 1Kohm resistor between OT speaker out leads.

View attachment 104950

Haven’t dived into troubleshooting yet, but I’ll gather some thoughts here:

• Bias was set hotter than before. Now over 60%, before it was way over under 40%, maybe even under 10%. Hard to say, I cannot recall pot setting. Could it be my output transformer is with low turns ratio and prefers super cold class B biasing? Or do non-isolated divided two sided bias circuit cross talk when bias set warm?
• Oscillation? Preamp grid resistors aren’t soldered near socket, but in input jacks with shielded wire leading to tube.
• Cutoff happening with gain. V2 and PI are missing input grid resistors. Blocking distortion somewhere before big bottles?
• Raising treble made note decay worse, bridging inputs brought more acceptable sound and cured note decay. HF Oscillation?
• Are my 2x15 speakers causing all this? Should test another cab before diving too deep.
• Maybe PI plate resistor balancing was bad choice? Is snubber cap necessary? Does MerlinB talk shit which I believed?

I really need an oscilloscope. Alixpress messed my order and never received one I ordered in june. Got money back, but didn’t place a new order… I’ll start with bias first.

Not the issue you are seeing but 270R 1W screen resistors seem really really low for both value and rating, especially for EL34s.

I had a 1.5K 5w burn up in my GT120 (also a quad of EL34s). The EL34 is hard on those. I have a 10w set ready to replace them if it happens again.

I’d keep that snubber on the PI plates.

Dumble used a pot to balance the PI on the ODS. I bought a handful of balanced tubes for PIs… that said I don’t think that is your issue. do you have some extra tubes you can swap in? Or even try swapping positions.

I’d change your bias back down just as a sanity check. I don’t see a glaring issue with the bias circuit. I know the diode has some resistance, is that and main cap enough of a RC filter? Do you see any major ripple on your meter?

I would try a grid stopper on the stage prior to PI first. One change at time, and then test.

I have a cheap FNIRSI 1014D scope with a HV probe but my own ADHD has stopped me from ever trying it on amps lol.

 

[JohnnyCreepy]

Not the issue you are seeing but 270R 1W screen resistors seem really really low for both value and rating, especially for EL34s.

I had a 1.5K 5w burn up in my GT120 (also a quad of EL34s). The EL34 is hard on those. I have a 10w set ready to replace them if it happens again.

I topped up screen resistor to 470R/5W year ago. Really should check ’em, thanks for heads up!

I’d keep that snubber on the PI plates.

Dumble used a pot to balance the PI on the ODS. I bought a handful of balanced tubes for PIs… that said I don’t think that is your issue. do you have some extra tubes you can swap in? Or even try swapping positions.

PI tube same as before, another plate resistor was topped from 81K to 100K and snubber was removed. Maybe triode halves are way off from balance and resistors need to be mismatched. I have extras, gonna tube roll first before taking things backwards.

I’d change your bias back down just as a sanity check. I don’t see a glaring issue with the bias circuit. I know the diode has some resistance, is that and main cap enough of a RC filter? Do you see any major ripple on your meter?

Good one to remember as before had high value cap there. Need to measure ripple and look what cutoff freq and resistor would be appropiate.

I would try a grid stopper on the stage prior to PI first. One change at time, and then test.

This should be the way…

I have a cheap FNIRSI 1014D scope with a HV probe but my own ADHD has stopped me from ever trying it on amps lol.

Probe ’em!

 

[Nostradoomus]

I really wish there was an option for amp kits in Canada. Don’t say Trinity, they are alway sold out and haven’t updated since last year

Might bite the bullet and order cross border but it seems like too much hassle in the current timeline :/

 

[Guardians of the analog]

I really wish there was an option for amp kits in Canada. Don’t say Trinity, they are alway sold out and haven’t updated since last year

Might bite the bullet and order cross border but it seems like too much hassle in the current timeline :/

What kind of amp would you be looking to build?

 

[Feral Feline]

I really wish there was an option for amp kits in Canada. Don’t say Trinity, they are alway sold out and haven’t updated since last year

Might bite the bullet and order cross border but it seems like too much hassle in the current timeline :/

Based out of Kuala Lumpur...

About - Ceriatone

For ordering purpose [email protected] Backup email address [email protected]

ceriatone.com

I was thinking of getting the Aunt Peg, because like you mentioned the Trinity Trip Top is always out of stock, especially those rare moments in time where I have money to get it.


At least with Ceriatone, you're not having to deal with Trumped up tariff charges.

 

[JohnnyCreepy]

I really wish there was an option for amp kits in Canada. Don’t say Trinity, they are alway sold out and haven’t updated since last year

Might bite the bullet and order cross border but it seems like too much hassle in the current timeline :/

If postage/import tax isn’t bad, this Finnish store could be an option. They have quite competitive pricing for amp kits: https://en.uraltone.com/kits/bass-amp-and-cab-kits.html

 

[Hal Harvey]

I really wish there was an option for amp kits in Canada. Don’t say Trinity, they are alway sold out and haven’t updated since last year

Might bite the bullet and order cross border but it seems like too much hassle in the current timeline :/

I agree with @Feral Feline Ceriatone is great option. I ordered and build a Dumble SSS kit from them. My recommendation would be to order with out transformers and then get Hammond/Heyboer equivalents. I'd also replace the included no name power supply caps with Nichicon/Rubicon/F&T. You get a great high quality chassis, faceplates are a bit meh, good layout documentation. You can order a head cab too.

Another non-US option is https://www.rosamp.com/shop-2/
They have full kits for SLO 30/50/100, JTM45, DR103, DR504, 5F2A.

London Power is a Canadian option for pre-amp kits. I read his Principles of Power almost 30 years ago haha. You would have to drill and label a chassis. https://londonpower.com/preamp-kit-selection/

What kind of amp would you be looking to build?

This, and why a kit?

Parts buying is easier than pedals IMO. If you want PCB based then Evolve (Australian) has some really cool options. They sell faceplates too (maybe for a Hammond chassis?). https://evolvediy.com/?post_type=product

 

[Guardians of the analog]

This, and why a kit?

Parts buying is easier than pedals IMO. If you want PCB based then Evolve (Australian) has some really cool options. They sell faceplates too (maybe for a Hammond chassis?). https://evolvediy.com/?post_type=product

Completely agree. Jason is a great guy to work with and very helpful with any questions. And his videos are excellent on youtube. Jason also has some great build docs as well.

 

[Asdrael]

You could also order from Europe. Shipping is usually not that bad. On top of my head Rosamp, Musikding, Tube Town and Tube Amp Doctor all sell kits of varying sizes, types and order of readiness. I think TAD even sells drilled chassis and headshells for their kits.

You could also get a PCB from somewhere with a BOM and go from there…

 

[Nostradoomus]

Marshall style most likely. The 2525 jubilee or 2202 from Ceriatone are looking pretty good to me right now. Getting a kit as it’s just dipping my toes in the diy amp world. And I know I would absolutely lose motivation if I had to source everything from multiple places

 

[Guardians of the analog]

Marshall style most likely. The 2525 jubilee or 2202 from Ceriatone are looking pretty good to me right now. Getting a kit as it’s just dipping my toes in the diy amp world. And I know I would absolutely lose motivation if I had to source everything from multiple places

Well if a 2202 is something your looking at, I can completely recommend the evolve diy origin replacement board. I've built two, one as a stock 2204 style and one as a Friedman dirty shirley. Fantastic project that's easy to get great results. I spent way less than a grand on each one.

 

[Feral Feline]

Marshall style most likely. The 2525 jubilee or 2202 from Ceriatone are looking pretty good to me right now. Getting a kit as it’s just dipping my toes in the diy amp world. And I know I would absolutely lose motivation if I had to source everything from multiple places

I sourced everything a la carte for my 5E3, with help from a friend.
My next amp I'll be doing the same thing, but only because a kit isn't offered for it.

There are a few kits out there I'd like to get...
Time. Money. Both in incredibly short supply right now.

 

[Guardians of the analog]

Time. Money. Both in incredibly short supply right now.

Man, I totally feel this. I would love to build more amps as I feel they are more fun to build, more fun to play and way more gratifying than pedals but they are expensive.

 

[Asdrael]

 

[Hal Harvey]

Working on the Wizard MTL lead channel preamp.

I was thinking I could make some PCBs for stuff I reuse, like when I was making the power supply board I could have left off some of the turrets but I was in the zone and just kept going. That board and the heater board could be PCBs...

I then was thinking about PCBs for the main boards too. I am so not a fan of tube sockets soldered into a PCB and then the PCB gets the stress. I saw some PCB tube sockets have chassis mounting wings. Is mounting the PCB to just the chassis mounted socket a thing? or is the idea you have correctly sized standoffs to mount both PCB and socket? I just can't imagine you would want the stress of a full board on the socket pins.

Fryette is a PCB guy and smart AF. I should creep some guts shots of his stuff.

 

[Asdrael]

View attachment 105088

Working on the Wizard MTL lead channel preamp.

I was thinking I could make some PCBs for stuff I reuse, like when I was making the power supply board I could have left off some of the turrets but I was in the zone and just kept going. That board and the heater board could be PCBs...

I then was thinking about PCBs for the main boards too. I am so not a fan of tube sockets soldered into a PCB and then the PCB gets the stress. I saw some PCB tube sockets have chassis mounting wings. Is mounting the PCB to just the chassis mounted socket a thing? or is the idea you have correctly sized standoffs to mount both PCB and socket? I just can't imagine you would want the stress of a full board on the socket pins.

Fryette is a PCB guy and smart AF. I should creep some guts shots of his stuff.

I am no Steve Fryette but using PCB Belton sockets for my stuff, the Novals do not have the flanges while the Octals do. You have to use standoffs (1mm for the noval and 1.5 for the octal is nice imo). It’s easy enough to fit enough standoffs on a PCB to avoid flex. Commercial products on pcb also usually have jacks and pots pcb mounted so that’s a few more anchor points tho.

 

[Nostradoomus]

Well if a 2202 is something your looking at, I can completely recommend the evolve diy origin replacement board. I've built two, one as a stock 2204 style and one as a Friedman dirty shirley. Fantastic project that's easy to get great results. I spent way less than a grand on each one.

Funny thing is I have an Origin already but it’s the little 5 watt fella.

 

[Guardians of the analog]

Funny thing is I have an Origin already but it’s the little 5 watt fella.

Well if you're looking to do the 20 watt version they can be found for 350-375 for a donor amp. That's the big stuff...chassis, head shell and trannies. I'm actually adding a 3 way bright cap to really make it the ultimate dirty Shirley. It's a simple build and I can help you navigate ordering parts

 

[Nostradoomus]

I’ll take a look around! @Guardians of the analog cheers

 

[Hal Harvey]

The Warlock (Wizard MTL lead channel) is alive.






I think this might be my cleanest build yet. It felt like everything was in its right place.

I actually had it running yesterday but my voltages were lower than the real thing. After knocking down one of the initial dropping resistors I have it sitting just above stock voltages, within 4-5% I think.

I ended up putting in NOS JAN 5751s in slots 1-3 (the actual MTL lead preamp) and left a JJ EC83S in the output position (the X88R driver follower output stage I have been putting in all the preamps).

The shift control is a switch in the real thing, basically it jumpers a 2nd slope resistor. I changed it to a fixed resistor and pot and boy am I glad I did. It really gives it a range of character, from scooped to THICC mids. I left off a boost switch that jumpers a resistor on a cathode bypass resistor on the 3rd stage. I just don't think it needs more gain, but it would be easy to drill a 1/4" hole and drop it in. TBD I guess.

It sounds great. I am excited to dual amp with the VH4 pre. I was playing it bone dry and the character felt a little boxy to me. That said I imagine it would sit in a mix perfectly. Hail Satan.