Search found 714 matches

by jjman
Wed Jun 21, 2017 11:35 pm
Forum: Technical Discussion
Topic: Help with load line for LTP phase inverter
Replies: 16
Views: 340

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.
by jjman
Thu Jun 15, 2017 11:53 pm
Forum: Trainwreck Discussion
Topic: Express Startup Issues
Replies: 15
Views: 333

Re: Express Startup Issues

Double check the measured value of the cathode resistor on v1a. If it is high those voltages would move in that direction.
by jjman
Sun Apr 30, 2017 11:27 pm
Forum: Trainwreck Discussion
Topic: Phase inverter issue on express build
Replies: 1
Views: 181

Re: Phase inverter issue on express build

Is B3 supposed to be that high? Are the power tubes installed? Did you double check the plate resistor values with a good meter?
by jjman
Thu Mar 30, 2017 11:56 pm
Forum: Technical Discussion
Topic: New amp build from old pa - transformer question...
Replies: 24
Views: 563

Re: New amp build from old pa - transformer question...

Some use the CT as one end. Many say it's taboo. Most talk about an "air gap" being needed. I think the issue is "saturation." (A bad kind.) Don't do it unless you know how to employ it that way.
by jjman
Wed Mar 29, 2017 1:51 am
Forum: Fender Discussion
Topic: VibroChamp / Pro Junior Boxy; Suggestions?
Replies: 11
Views: 407

Re: VibroChamp / Pro Junior Boxy; Suggestions?

The trem on the homebrew provides the "ground" connection to a Larmar Post PIMV on a ~5E3~ output.
by jjman
Tue Mar 28, 2017 1:48 am
Forum: Technical Discussion
Topic: 1974 Traynor YGM-3 Guitar Mate Reverb
Replies: 17
Views: 519

Re: 1974 Traynor YGM-3 Guitar Mate Reverb

PR Trem is an AC signal thru a cap to the bias, so it pushes the bias up and down. I think all non-photo-resistor trems push and pull. Photos just pull down.
by jjman
Sun Mar 26, 2017 5:21 pm
Forum: Fender Discussion
Topic: twin reverb bias question
Replies: 28
Views: 607

Re: twin reverb bias question

I made that mistake once. Very frustrating. The internets tell us to use the bulb for initial startups but fail to remind us that we must stop using the bulb for any quantitative testing.
by jjman
Sun Mar 26, 2017 5:11 pm
Forum: Fender Discussion
Topic: VibroChamp / Pro Junior Boxy; Suggestions?
Replies: 11
Views: 407

Re: VibroChamp / Pro Junior Boxy; Suggestions?

Tremolux AA763 trem is the roach type. You won't have the negative bias to send to the trem, to keep it "off," which is only one "issue" with using that trem in a VC type build. I like all Fender trems. The only drawback with the VC trem is the fact its intensity control also changes the bias of the...
by jjman
Fri Mar 24, 2017 11:49 pm
Forum: Fender Discussion
Topic: twin reverb bias question
Replies: 28
Views: 607

Re: twin reverb bias question

How is the heater voltage during these tests. Does it change measurably?
by jjman
Sat Mar 11, 2017 4:38 pm
Forum: Technical Discussion
Topic: 6SJ7 Pentode Operating Conditions
Replies: 51
Views: 1421

Re: 6SJ7 Pentode Operating Conditions

With the original goal of allowing for better pedal response I wonder if addressing the load on the pedals, while preserving the grid-leak bias, should be considered? My Silvertone 1451 has a single stage grid-leak-biased pentode preamp into the power tube. And it presents very close to a 1meg load ...
by jjman
Sat Feb 25, 2017 3:56 pm
Forum: Fender Discussion
Topic: 1967 "Fender" Double Bassmaster Custom Amp
Replies: 31
Views: 935

Re: 1967 "Fender" Double Bassmaster Custom Amp

Looks like a great platform for whatever you want to do with it. The only concern I see is the gauge of the orange heater wire looks a little thin.
by jjman
Tue Oct 25, 2016 12:40 am
Forum: Fender Discussion
Topic: Fender BF Tremolo Disconnect
Replies: 11
Views: 765

Re: Fender BF Tremolo Disconnect

If one experiments with master volumes before and after the LTP, it might be preceived that moving the ratio of distortion away from the pre-amp towards the power amp is a good thing. The reverb channel of a 2 channel BF Fender sounds awful when it overdrives, as the 1st point of the pre-amp to ove...
by jjman
Thu Sep 29, 2016 12:05 am
Forum: Technical Discussion
Topic: Spark on reverb transformer.
Replies: 8
Views: 615

Re: Spark on reverb transformer.

Looking at a scheme I never thought that this is the same as an OT, as mentioned, regarding flyback. Why have the internets not warned us on this like with that other tranny?
by jjman
Sun Sep 25, 2016 3:54 pm
Forum: Technical Discussion
Topic: 1st mod = learning the hard way
Replies: 27
Views: 1949

Re: 1st mod = learning the hard way

Using mixing resistors will weaken the voltage of each signal 50% from the voltage division. (This is less then a 50% reduction in "volume.") Injecting each preamp in to opposite sides of a LTPI preserves the full strengths. Look at an 18watt Marshall on how to do it. If using pre PI MVs, it won't m...
by jjman
Tue Aug 09, 2016 11:44 pm
Forum: Technical Discussion
Topic: Installing Strain Relief. Your method please!
Replies: 14
Views: 1079

Re: Installing Strain Relief. Your method please!

I place the relief, with the cord in it, into my bench vise. I leave it tight for a while, rotating it a few times. Then I use vise grips to keep it closed and transfer it for installation.