Search found 730 matches

by jjman
Sun Feb 18, 2018 11:43 pm
Forum: Technical Discussion
Topic: Random Acts of Stupidity
Replies: 8
Views: 221

Re: Random Acts of Stupidity

When I built my 1st amp it was about 23 years ago. It’s a 5F1 Champ circuit and there was only one problem. Huge hum that increased with the volume control. I had read about proper grounding but this chassis is so small I didn’t pay too much attention. And there were no websites related to amps back...
by jjman
Fri Feb 02, 2018 12:55 am
Forum: Trainwreck Discussion
Topic: small mods to make an Express pedal friendly
Replies: 4
Views: 199

Re: small mods to make an Express pedal friendly

If you have the amp set low enough to not be clipping, it is already in pedal-friendly mode. The un-friendliness occurs if the preamp is clipping somewhere and certain effects are in the front and not a loop. In this case the loop has to be after the 3rd preamp stage since that clips. The 1st two pr...
by jjman
Tue Jan 23, 2018 1:52 am
Forum: Technical Discussion
Topic: Monkeymatic Black Butte (univalve build)
Replies: 49
Views: 4191

Re: Monkeymatic Black Butte (univalve build)

Very cool and PTP rules. How is the ping thing? Did you try moving both the main filter grounds and the HV CT to a "star" via home runs? Those show "daisyed" too.
by jjman
Sat Jan 06, 2018 4:23 pm
Forum: Technical Discussion
Topic: Just learned of this site... here's my current project. Another rusty old PA amp
Replies: 26
Views: 1306

Re: Just learned of this site... here's my current project. Another rusty old PA amp

The impedance of the OPT needs to be determined unless that is marked somewhere. I'd be concerned about potential bass from the OPT but it doesn't look too small and may be fully adequate. You could make just about anything with all those holes sockets available. Are the smaller holes sized for smal...
by jjman
Sun Dec 10, 2017 7:18 pm
Forum: Technical Discussion
Topic: Skipping the PT?
Replies: 15
Views: 608

Re: Skipping the PT?

One of the sites I frequent forbids posting schematics using that approach, even with a disclaimer. They probably also forbid discussing a new build using it. Of course each site can make its own rules.
by jjman
Thu Nov 30, 2017 1:29 am
Forum: Fender Discussion
Topic: 73 Quad Reverb 100w. 'Restoration' into a head cab
Replies: 13
Views: 782

Re: 73 Quad Reverb 100w. 'Restoration' into a head cab

Yeah the 100W Super Six Reverb, 100W Twin Reverb, 100W Quad Reverb, 100 W Bassman Reverb, 100W Vibrasonic Reverb and 100W Dual Showman Reverb from the same era, all used basically the same amp, same chassis, same boards/parts, same trannies etc, but with different faceplates, and combinations of sp...
by jjman
Wed Nov 15, 2017 12:56 am
Forum: Trainwreck Discussion
Topic: My Liverpool Experiment
Replies: 16
Views: 926

Re: My Liverpool Experiment

No more class A EL84 with B+ voltages over 280-300V. AC30, TW, all DR Z, Matchless, BadCat amps all are class AB amps with silly overbiased EL84. "Class A" marketing hype on these tube eaters ;) I pushed my 2xel84 amp down to 265 volts on the plate via a dropper off the rectifier. 44ma each. Not ev...
by jjman
Tue Oct 24, 2017 11:35 pm
Forum: Technical Discussion
Topic: One stop shopping?
Replies: 10
Views: 418

Re: One stop shopping?

Here's my compilation in my bookmarks. Many are old. Allen Amplification Amp Maker - Guitar amp kits Amplates.com Amplified Parts Angela Instruments Online Catalog Antique Electronic Supply Apex Jr. Supplies BYOC CE Distribution (Wholesale) CeriaTone.Com - DIY Guitar Tube Amp ClassicTone Transformer...
by jjman
Sun Oct 15, 2017 2:08 pm
Forum: Technical Discussion
Topic: Help with switchable cathode resistor
Replies: 13
Views: 519

Re: Help with switchable cathode resistor

"B" looks better since there is no chance for a period of time with the cathode-path "open." But I'm thinking both would cause at least some "pop."
by jjman
Tue Sep 26, 2017 11:54 pm
Forum: Technical Discussion
Topic: mixing resistors
Replies: 12
Views: 535

Re: mixing resistors

I recently converted an amp from a pre-PI mixer (pot) setup to injecting into both PI grids. The “channels” (actually a parallel loop situation,) are out of phase. I had a phase flipping tiny transformer on the loop side with the mixer-pot setup, but I wanted more potential post-return loop signal. ...
by jjman
Sun Sep 24, 2017 10:02 pm
Forum: Technical Discussion
Topic: Problem with biasing Twin reverb type amp
Replies: 20
Views: 767

Re: Problem with biasing Twin reverb type amp

Placing the meter in the current path, as THAT probe does, means the meter's internal resistance skews the measurement. Even a quality meter can have that issue. Transformer Shunt Method also has that issue. Using the transformer-voltage-drop method or the cathode-resistor-voltage-drop method avoids...
by jjman
Sat Sep 16, 2017 3:37 pm
Forum: Technical Discussion
Topic: Supro s6424 build
Replies: 20
Views: 1185

Re: Supro s6424 build

For both I would try the 1megs alone 1st. Then add the resistor if it doesn't seem right.
by jjman
Sun Sep 10, 2017 5:30 pm
Forum: Technical Discussion
Topic: Bias tweaker or "touch"
Replies: 6
Views: 520

Re: Bias tweaker or "touch"

I'm not understanding why that adjuster would affect the idle current with the LFO off. Maybe some DC is leaking thru the LFO coupler?
by jjman
Wed Sep 06, 2017 12:13 am
Forum: Technical Discussion
Topic: Output impedance tolerance?
Replies: 5
Views: 356

Re: Output impedance tolerance?

For tube amps it is safer to use a speaker with a "too low" impedance vs a "too high" impedance. For solid state is it the opposite. The risk depends on the output tranny and the amount of signal pushed. There is a consensus opinion on the internet that it is safer with a vintage Fender than a vinta...
by jjman
Wed Jul 12, 2017 11:45 pm
Forum: Technical Discussion
Topic: What to clean a chrome chassis with, that won't remove the lettering.
Replies: 7
Views: 504

Re: What to clean a chrome chassis with, that won't remove the lettering.

I use Nu-Finish on crome chassis. Hand polish and buff. No wax or residuals AFAIK.