Search found 23 matches

by dpin
Thu Aug 16, 2018 3:18 pm
Forum: Fender Discussion
Topic: Modded Super Reverb Reissue - HELP
Replies: 5
Views: 1299

Re: Modded Super Reverb Reissue - HELP

Adding NFB can effect the highs also so if you find that the bass tightens up but you don't love the effect it has on the highs you "could" add a cap to the circuit, like in a presence control. Your tech should be able to figure that out.
by dpin
Wed Aug 15, 2018 12:47 am
Forum: Fender Discussion
Topic: Modded Super Reverb Reissue - HELP
Replies: 5
Views: 1299

Re: Modded Super Reverb Reissue - HELP

For the treble you can try adding a snubber cap across the PI plates from pin 1 to 6 (snip attached). Anywhere from 10pf up to 100pf could be useable. For the bass you might try increasing NFB by adding the same value (820 ohm) in parallel across the NFB resistor. It might take going lower with the ...
by dpin
Thu Nov 02, 2017 3:18 pm
Forum: Dumble Files
Topic: High filter switch option
Replies: 0
Views: 17550

High filter switch option

I had a couple of these Radio Shack 6 position rotary switches sitting around and decided to use 2 of them for the SSS filters. The bass filter wiring was simple and predictable, but I had to take a second to figure out how to do the treble switch. I have seen where the use of a different switch req...
by dpin
Fri Sep 15, 2017 11:53 pm
Forum: Dumble Discussion
Topic: Help! Amp Issue Started Today
Replies: 13
Views: 1600

Re: Help! Amp Issue Started Today

What AC voltage reading are you getting feeding the rectifier? (345-0-345 on the layout)

Clip one meter lead to ground, set to AC and measure each leg going into the diodes with the amp in standby
by dpin
Fri Sep 15, 2017 11:32 pm
Forum: Dumble Discussion
Topic: Help! Amp Issue Started Today
Replies: 13
Views: 1600

Re: Help! Amp Issue Started Today

Is your first filter cap after the rectifier a single cap or 2 series stacked caps?
by dpin
Wed Sep 13, 2017 4:47 pm
Forum: Fender Discussion
Topic: Twin Master Volume Modifications?
Replies: 6
Views: 1173

Re: Twin Master Volume Modifications?

Here's 3 easily reversible moves to drop some db's and retain "headroom"
- Pull 2 6L6's
- Add a switch so you can drop one speaker when you pull those tubes
- Replace the PI tube with a 12AU7
by dpin
Wed Sep 13, 2017 2:35 pm
Forum: Trainwreck Discussion
Topic: can I use 5v rectifier heater tap for fender jewel lamp?
Replies: 2
Views: 561

Re: can I use 5v rectifier heater tap for fender jewel amp?

Yes, perfectly OK to do.
I have done it quite a few times and the lamp will just glow slightly less bright, hardly noticeable.
by dpin
Tue Sep 05, 2017 7:56 pm
Forum: Marshall Discussion
Topic: Marshall JCM 2000 DSL 50 mods
Replies: 19
Views: 6331

Re: Marshall JCM 2000 DSL 50 mods

I brought this over for the sake of discussion.
If this is the actual schematic you should be able to dial in the mids here.
I chose this snippet because you mentioned working the C12 -bright cap off the red channel, so I am assuming this is the red channel
by dpin
Tue Sep 05, 2017 7:14 pm
Forum: Marshall Discussion
Topic: Marshall JCM 2000 DSL 50 mods
Replies: 19
Views: 6331

Re: Marshall JCM 2000 DSL 50 mods

I see now that the same designations appear on the 2 different pages. (i.e. C12 page 7 = Rk, C12 page 1 = bright cap)
And, since there is a separate tone stack for the red channel, you should be able to dial in the mids there, and not effect the green
by dpin
Tue Sep 05, 2017 12:41 pm
Forum: Marshall Discussion
Topic: Marshall JCM 2000 DSL 50 mods
Replies: 19
Views: 6331

Re: Marshall JCM 2000 DSL 50 mods

If you plan on keeping the AU7 in the PI you might want to change out the shared cathode resistor to approx. 2.7k to keep it close to center biased. With stock values it's biased very hot. By center biasing you will allow the biggest input signal before clipping. You can experiment with the mid cap ...
by dpin
Sat Sep 02, 2017 11:59 pm
Forum: Marshall Discussion
Topic: Marshall JCM 2000 DSL 50 mods
Replies: 19
Views: 6331

Re: Marshall JCM 2000 DSL 50 mods

Yes, you are correct that most amps, even beyond Marshalls, have a 12AX7 PI. I see it as a homogenization of topology, in that, everyone does it because it works and always has. I look at mods and custom amp builds from a stance of "how can I make an amp that will fulfill this particular players nee...
by dpin
Fri Sep 01, 2017 8:24 pm
Forum: Marshall Discussion
Topic: Marshall JCM 2000 DSL 50 mods
Replies: 19
Views: 6331

Re: Marshall JCM 2000 DSL 50 mods

Super simple 'mod' Try replacing the 12AX7 phase inverter with a 12AT7 It will effect both channels, but you might even wind up liking it better for the green channel. It has tamed a couple high gain builds for me and I now include it in the original plan. You wouldn't believe how much clipping happ...
by dpin
Fri Sep 01, 2017 1:06 am
Forum: Trainwreck Discussion
Topic: Rockster Oscillation Woes
Replies: 8
Views: 1146

Re: Rockster Oscillation Woes

When you temporarily removed the PPIMV what value did you have for grid reference Rg before the power tubes?
by dpin
Thu Aug 31, 2017 8:13 pm
Forum: Fender Discussion
Topic: Fender PA 100 questions
Replies: 4
Views: 866

Re: Fender PA 100 questions

I'm still using mine for vocals at rehearsal but every once in a while I give it a certain look when I walk by. That amp is begging for 4 separate simple preamps to feed into a common PI. I picture the signal paths all being in phase so you could use one of these amp selector pedals and combine chan...
by dpin
Thu Jul 03, 2014 3:00 am
Forum: Dumble Discussion
Topic: Has anybody tried a 250kA OD Level in a Low Plate Classic?
Replies: 42
Views: 6650

Re: Has anybody tried a 250kA OD Level in a Low Plate Classic?

http://www.youtube.com/watch?v=rl7sg8XqFIU How is this guy getting this level of gain(distortion) out of a Dumble with a Strat (3:06)? CW Your idea of increasing the trimmer to 250K will get you a little closer. There are also a couple of "clip ins" that you could try to increase OD without solderi...