Search found 118 matches

by pureoldsound
Tue Mar 21, 2023 12:11 am
Forum: Marshall Discussion
Topic: Marshall plexi built treble issues
Replies: 20
Views: 3334

Re: Marshall plexi built treble issues

pureoldsound wrote: Tue Mar 21, 2023 12:08 am Added the pic. The amp does have grid stoppers. 33k input 470k for V2. Just like a marshall plexi.
by pureoldsound
Tue Mar 21, 2023 12:08 am
Forum: Marshall Discussion
Topic: Marshall plexi built treble issues
Replies: 20
Views: 3334

Re: Marshall plexi built treble issues

Added the pic. The amp does have grid stoppers.
by pureoldsound
Tue Mar 21, 2023 12:07 am
Forum: Marshall Discussion
Topic: Marshall plexi built treble issues
Replies: 20
Views: 3334

Re: Marshall plexi built treble issues

pureoldsound wrote: Sun Mar 12, 2023 9:57 pm This is the amp
by pureoldsound
Sun Mar 19, 2023 8:24 pm
Forum: Marshall Discussion
Topic: Marshall plexi built treble issues
Replies: 20
Views: 3334

Re: Marshall plexi built treble issues

Alright, so I tried the snubber approach with a 50pf cap I have here (I don’t have a 7pf). It looks like everything boils down to V2 pin 1 and 2. Tried the snubber in all other pins (V1 and v2) and it cures it in V2 pin 1 and 2. Since I have the issue on pin 6 and 7. The culprit could be that I have...
by pureoldsound
Sun Mar 19, 2023 7:05 pm
Forum: Marshall Discussion
Topic: Marshall plexi built treble issues
Replies: 20
Views: 3334

Re: Marshall plexi built treble issues

Just an update. I made my lead dress shorter going from volume pots to board. Still the same issue. Took My hook up wire off installed shielded wire on volume pots, switch and cap routing. Still the same problem. I have an internal jumper of channels, disconnected those wires. Still the same issue. ...
by pureoldsound
Sun Mar 12, 2023 11:39 pm
Forum: Marshall Discussion
Topic: Marshall plexi built treble issues
Replies: 20
Views: 3334

Re: Marshall plexi built treble issues

What you have is basically Arecibo. You can hear the inception of the Universe from your amp! Hehehehe, :lol: well, if the problem is shielded wiring I can work on that. I use to built a model that had TW express pre-amp and I remembering using shielded wiring. Thought this amp will not have that i...
by pureoldsound
Sun Mar 12, 2023 10:25 pm
Forum: Marshall Discussion
Topic: Marshall plexi built treble issues
Replies: 20
Views: 3334

Re: Marshall plexi built treble issues

sluckey wrote: Sun Mar 12, 2023 10:13 pm That's a whole lot different from my Plexi! I don't know if what I said applies to your amp or not. Can you provide an as-built schematic?
It has a few bells and whistles but it is basically a Plexi.
by pureoldsound
Sun Mar 12, 2023 9:57 pm
Forum: Marshall Discussion
Topic: Marshall plexi built treble issues
Replies: 20
Views: 3334

Re: Marshall plexi built treble issues

This is the amp
by pureoldsound
Sun Mar 12, 2023 9:52 pm
Forum: Marshall Discussion
Topic: Marshall plexi built treble issues
Replies: 20
Views: 3334

Re: Marshall plexi built treble issues

No I am not getting DC anymore after the tone cap was installed. You don't need a cap leading into the tonestack. That's just a Band-Aid fix. One (or more) of the three tonestack caps are leaky. Ahhhh I was afraid of that with these old cap. I thing I may be able to narrow it done. I think is the o...
by pureoldsound
Sun Mar 12, 2023 9:15 pm
Forum: Marshall Discussion
Topic: Marshall plexi built treble issues
Replies: 20
Views: 3334

Re: Marshall plexi built treble issues

Thanks for the reply. No I am not getting DC anymore after the tone cap was installed. I used a mix of schematics , but mainly a 1968 50w schematic. Thought about oscillation. But it is stranged that the problem goes away after I add the mid and bass. I will chop stick V2 and see if it helps. I’ll t...
by pureoldsound
Sun Mar 12, 2023 7:54 pm
Forum: Marshall Discussion
Topic: Marshall plexi built treble issues
Replies: 20
Views: 3334

Marshall plexi built treble issues

Hey all, I built a Marshall plexi style amp 50w about 1yr or so ago. After the built process , for some reason I was getting DC voltage into my tone stack so I added a 500pf cap (tone cap), however, it seems that this value was too small as it cut all my lows and mids. So I added a 0.47uf and all my...
by pureoldsound
Sat Dec 17, 2022 4:08 pm
Forum: Technical Discussion
Topic: "Blows Fuses" Debugging
Replies: 29
Views: 43142

Re: "Blows Fuses" Debugging

Fixed it . I use Ken’s trick with the diodes in series at the PW tubes. It turns out one set was burned and could not see it due to the heat shrink disconnected both and it did not blow the fuse.

It turns out it wasn’t the ot, pt or the pw caps.

I’ll save those for another project then.
by pureoldsound
Mon Dec 12, 2022 3:25 am
Forum: Technical Discussion
Topic: "Blows Fuses" Debugging
Replies: 29
Views: 43142

Re: "Blows Fuses" Debugging

Well,

Just a follow up. It turns out is not the PT, OT, power caps. Changed the switches, and it still blowing the main fuse?
by pureoldsound
Mon Jul 11, 2022 1:26 pm
Forum: Technical Discussion
Topic: "Blows Fuses" Debugging
Replies: 29
Views: 43142

Re: "Blows Fuses" Debugging

martin manning wrote: Mon Jul 11, 2022 5:56 am That’s normal if you have a grounded center tap on the heater winding and you are measuring from the heater pins to ground. Measuring across the heaters you will get 6.66 VAC.

Thanks Martin….
by pureoldsound
Mon Jul 11, 2022 3:53 am
Forum: Technical Discussion
Topic: "Blows Fuses" Debugging
Replies: 29
Views: 43142

Re: "Blows Fuses" Debugging

It always measured 3.33v