Search found 25 matches

by badfan
Sun Aug 10, 2014 12:17 pm
Forum: Technical Discussion
Topic: Grid voltage problem.....
Replies: 6
Views: 817

Re: Grid voltage problem.....

Guys, added the resistor (1Meg) and works great..... thanks very much.
by badfan
Sun Aug 10, 2014 11:45 am
Forum: Technical Discussion
Topic: Grid voltage problem.....
Replies: 6
Views: 817

Re: Grid voltage problem.....

ahhhh..... I see what you mean, after the V2 2nd stage, before V3 etc pin7, (also noticed the diagram is slightly incorrect, should connect to b1 pole go b3 on DPDT switch)......

Is there a preferred value for the resistor, or just go with the standard 470k?

Thanks again... appreciate it
by badfan
Sun Aug 10, 2014 11:16 am
Forum: Technical Discussion
Topic: Grid voltage problem.....
Replies: 6
Views: 817

Grid voltage problem.....

Hi everyone, I am building a dual channel amp (for my son) which is effectively based on having a Marshall (2204) and Soldano (lead) channel (25th birthday present for |September this year...) I have attached the circuit diagrams for reference... as you can see nothing too difficult... (uses mechani...
by badfan
Tue Apr 07, 2009 10:05 am
Forum: Technical Discussion
Topic: Advice needed on homebrew amp
Replies: 0
Views: 4308

Advice needed on homebrew amp

Guys Excellent forum by the way... I have recently built anamp (schematic attached) and in summary I am really pleased with how this one has turned out. Excellent sound / response / medium gain / tone etc. I am not the most technically advanced amp builder or experienced so I have a few questions fo...
by badfan
Fri Jan 30, 2009 3:50 pm
Forum: Technical Discussion
Topic: Fender 94 Twin Amp - Problem
Replies: 7
Views: 4041

Re: Fender 94 Twin Amp - Problem

OK some futher info... That scratchy sound is also still present when I take all pre-amp tubes so the problem must be in the BIAS,power amp section - right? I just did'nt here that much before as it was a lot more prominant when the pre-amp was connected, now that I am using the scope I am seeing it...
by badfan
Fri Jan 30, 2009 3:30 pm
Forum: Technical Discussion
Topic: Fender 94 Twin Amp - Problem
Replies: 7
Views: 4041

Re: Fender 94 Twin Amp - Problem

Thanks for the help so far.... Where I am now is there are 2 distinct problems, the humming and the dodgy V7B stage. I think I have found the problem of the humming. I have got the oscilloscope out and I am reading a small AC signal via the BIAS circuit being injected into pin 5 of the power tubes b...
by badfan
Mon Jan 26, 2009 6:15 am
Forum: Technical Discussion
Topic: Fender 94 Twin Amp - Problem
Replies: 7
Views: 4041

Re: Fender 94 Twin Amp - Problem

Thanks Guys

I will try out the suggestions and let you know how I get on. Suffice to the layout and design on this one is a bit of a pig...

Cheers
Sean
________
Zx14 vs hayabusa
by badfan
Sun Jan 25, 2009 4:01 pm
Forum: Technical Discussion
Topic: Fender 94 Twin Amp - Problem
Replies: 7
Views: 4041

Fender 94 Twin Amp - Problem

Hi Everyone Looking for some wisdom... I have picked up a Fender 94 Twin Amp that has a problem in that when you switch it on theres an intermittent "scratchy" sound that does not shut up. I have done the standard isolation stuff and have traced the problem to what I believe to be the first stage of...
by badfan
Tue Sep 09, 2008 5:49 pm
Forum: Technical Discussion
Topic: Marshall 2144 - questions and advice required?
Replies: 8
Views: 4520

Re: Marshall 2144 - questions and advice required?

Guys, I think you both summed it up nicely and i'm definately sold. Decision made I am going to build one of these pre-maps, and probably mate it with a 2x6v6 output stage to start with as what as been pointed out. a lot of the 'good' sound from this amp does come from the pre-amp section and I like...
by badfan
Tue Sep 09, 2008 3:16 pm
Forum: Technical Discussion
Topic: Marshall 2144 - questions and advice required?
Replies: 8
Views: 4520

Re: Marshall 2144 - questions and advice required?

Hi Casey, Thanks again for the comments really helpful. Thankfully I am up to speed with amp topology and understanding cascaded vs parellel and the Marshall low/high gain approach for this type of amp. What i was struggling with was the series approach for the cathode connections i.e. why and what ...
by badfan
Tue Sep 09, 2008 8:10 am
Forum: Technical Discussion
Topic: Marshall 2144 - questions and advice required?
Replies: 8
Views: 4520

Re: Marshall 2144 - questions and advice required?

b) The boost function is permanently switched on. Is the original footswitch present? It sounds like a hardwired fix for a lost or broken footswitch. 1) In terms of the pre-amp I understand most things but the boost function has me foxed? I am not to sure how this is working if you see it has a .04...
by badfan
Mon Sep 08, 2008 9:22 pm
Forum: Technical Discussion
Topic: Marshall 2144 - questions and advice required?
Replies: 8
Views: 4520

Marshall 2144 - questions and advice required?

Guys Recently I have come across a Marshall 2144 amp (made between 1978/1979 which is different from the normal pre JCM800 Marshall master volume type amps in that it has a reverb, boost/reverb pedal function and the placement of the tone circuit is not the standard cathode follower type. I have att...
by badfan
Mon Sep 08, 2008 8:56 pm
Forum: Technical Discussion
Topic: Problem.... or not? - red plating issue - advice appreciated
Replies: 13
Views: 1949

Re: Problem.... or not? - red plating issue - advice appreciated

Guys Guess what sussed it.... turns out there was a connection to the OT secondary ground connection from pin 8 on V4. Obviously when I installed a resistor from pin 1 to ground I did not notice the connection on pin 8 which I should have removed? must be getting old or going blind :oops: Anyway I h...
by badfan
Mon Sep 08, 2008 8:55 pm
Forum: Technical Discussion
Topic: Problem.... or not? - red plating issue - advice appreciated
Replies: 13
Views: 1949

Re: Problem.... or not? - red plating issue - advice appreciated

Guys Guess what sussed it.... turns out there was a connection to the OT secondary ground connection from pin 8 on V4. Obviously when I installed a resistor from pin 1 to ground I did not notice the connection on pin 8 which I should have removed? must be getting old or going blind :oops: Anyway I h...
by badfan
Mon Sep 08, 2008 7:08 pm
Forum: Technical Discussion
Topic: Problem.... or not? - red plating issue - advice appreciated
Replies: 13
Views: 1949

Re: Problem.... or not? - red plating issue - advice appreciated

Here are the DC resistance readings from the OT with both power tubes pulled and no speaker load on the secondary Primary (brown = CT) Red-brown = 43.4 ohms White-Brown = 44.6 ohms Red-White = 87.9 ohms Secondary (orange = ground) Yellow-Orange = 0.4 ohms Green-Orange = 0.6 ohms Grey-Orange = 0.8 oh...