Search found 758 matches

by jjman
Tue Jan 23, 2018 1:52 am
Forum: Technical Discussion
Topic: Monkeymatic Black Butte (univalve build)
Replies: 49
Views: 6794

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: 29
Views: 2923

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: 1461

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: 15
Views: 2273

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: 2190

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: 854

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: 1361

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: 1781

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: 2219

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: 2316

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: 759

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: 623

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: 980

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.
by jjman
Mon Jul 10, 2017 11:39 pm
Forum: Fender Discussion
Topic: Static in reverb channel of '74 Deluxe Reverb
Replies: 5
Views: 918

Re: Static in reverb channel of '74 Deluxe Reverb

My '71 had board conduction where the 5 leads join that include the wire to the V4A grid. Faint crackling. I added a standoff to float that node off the board. Pressing the vicinity with a chopstick revealed it. (I modded the values of the 10pf/3.3meg to 47pf/1meg for more signal.)
by jjman
Wed Jun 21, 2017 11:35 pm
Forum: Technical Discussion
Topic: Help with load line for LTP phase inverter
Replies: 20
Views: 2851

Re: Help with load line for LTP phase inverter

Since you are not averse to employing SS devices to the PI you could check on using a Constant Current setup on the tail. I don't know if those force more balance but it's worth checking.