Tube Amp Archive

I'd posted a while back about potential changes to my JTM45 clone to decrease bass. Since then, I made a few changes and am pleased with the results. A little background on this amp first. In 2017 I was gifted $500 to my customer account at AES (Antique Electronic Supply). I live 4 miles from there ...

I seem to prefer smallish output coupling caps in my own designs, but have a Bassman with 0.1uF output caps and it isn't too tubby. This has also been my experience with 100nF couplers coming out of the PI. IMO it really depends on where your amp is running into issues. I agree with Martin about th...

The other place to trim bass would be reducing the cathode bypass cap on V1. I hadn't thought about that but will give it a try. The circuit is built on a turret board so making changes is easy and reversable. I'm going to build a simple amp chassis stand using some good birch plywood I have so I c...

Those proposed changes all sound reasonable. I seem to prefer smallish output coupling caps in my own designs, but have a Bassman with 0.1uF output caps and it isn't too tubby. I run EL34s in that amp. Any reason you want to switch to 5881s from KT66s? Just too bassy? I don't have experience with t...

I built a JTM45 clone 7 years ago. It has too much bottom end for me. I keep the bass at 0. I thought I'd change out the 0.1 coupling caps to the OP tubes to .022 as a starting point to reduce low end. I've also always had KT66s in it and am going to replace them with current production Tungsol 5881...

I was pulling 81ma out of it for a 6550 prior to upgrading to an AnTek Toroidal. Used maybe about 6 months. It was admittedly hard to tell if it was sagging under demand as my output transformer was also a 5k 125SE Hammond OT which is only 15w and bass wasn't the greatest. PT never gave any gripes ...

I may try that. I designed the MOD102 that AES/CE Distribution sells as a kit. The first version tapped DC off the output tube cathode applied to the filaments instead of the split 100 ohm resistors to ground on the second version. I never took the time to compare the two.

casey73 wrote: ↑Wed Nov 20, 2024 1:43 am

xtian wrote: ↑Tue Nov 19, 2024 3:39 pm Pull the power tubes out and listen for hum. If none, it's not the PT/OT arrangement.

Good point. I'll try that

Pulled the output tube and hum disappeared so it's just the inherent hum SE class A amps are prone to, not inductive hum.

xtian wrote: ↑Tue Nov 19, 2024 3:39 pm Pull the power tubes out and listen for hum. If none, it's not the PT/OT arrangement.

Good point. I'll try that

Do you have the funds and the room for a separate filament transformer? That would drop the temperature of the PT a nice amount and extend its life if your pushing its limits. I have several small NOS 1.2A 6.3 transformers, however, the 269EX filament winding is rated 2.5 amps. Something to conside...

I worked for CE Distribution for 12 years and purchased two MOD102+ kits before I retired in 2019. I built one while still working there but made some changes to it. I installed an IEC socket, used better 22 AWG PVC wire instead of the 20 gauge cloth covered wire that comes with it, put large rubber...

WhopperPlate wrote: ↑Tue Oct 24, 2023 4:27 pm Love the look of those old behemoths

They do look cool but they are a beast to haul around.

Stevem wrote: ↑Tue Oct 24, 2023 10:12 am Yes, that's a code number of manufacturer.
It was made on the 36th week of 1979.

Thanks much for the info. I put the EV in a 1-12 cabinet I have.

I bought a very old EVM12-L from a guy I worked with years ago. There is no decal on it but I've owned other EVM12-L in the past. It has a heat sink screwed to the back. The only marking on it is 936. The frame is painted black. Since it's a 200 watt speaker and I don't have any amp over 100 watts I...

I know that there are maximum filter capacitor rules when following a rectifier tube. My current project will use a 5AR4 and 60UF is the recommended maximum capacitor immediately following it. Are there any "rules of thumb" regarding the maximum capacitor values down line from the plate supply?