Search found 711 matches

by jjman
Thu Mar 30, 2017 11:56 pm
Forum: Technical Discussion
Topic: New amp build from old pa - transformer question...
Replies: 24
Views: 416

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: 303

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: 425

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: 453

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: 303

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: 453

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: 1167

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: 759

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: 684

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: 561

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: 1855

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: 1011

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.
by jjman
Wed Jul 06, 2016 11:36 pm
Forum: Fender Discussion
Topic: Bandmaster reverb (i think 1974)
Replies: 5
Views: 821

Re: Bandmaster reverb (i think 1974)

I think the 100wt Fenders had a Master in 1971. Drawing # 010182 Rev F is dated 11/17/71 and was not the 1st MV series since it has the boost. Drawing ver C would be earlier, does not have the boost, DOES have the MV, but is not dated:
by jjman
Thu Jun 23, 2016 11:50 pm
Forum: Technical Discussion
Topic: Phase Inverter Distortion
Replies: 5
Views: 556

Re: Phase Inverter Distortion

It is increasing the "load." Similar to increasing the load in a truck. Poorer acceleration and deceleration.
by jjman
Wed May 11, 2016 12:25 am
Forum: Technical Discussion
Topic: Grid Resistor Value Determinations
Replies: 11
Views: 1452

Re: I'll look at the information you posted

............Another question- If there is no substantial current flowing in the bias circuit, how do different value bias feed resistors affect the bias on the output tubes? ..............silverfox. The flow of current in the bias circuit does not flow thru the grid / bias feed resistors. The bias ...