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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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Thread Tools |
4th May 2012, 2:12 pm | #41 | |
Octode
Join Date: Aug 2008
Location: Rayleigh near Southend-On-Sea, Essex, UK.
Posts: 1,883
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Re: RSC Guitar Amplifier.
Hi Colin,
Quote:
I’ve have had problems where point to point prototypes worked fine and I’ve had subsequent problems when the circuit is transformed to a neat tag or a PCB layout! Terry. |
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5th May 2012, 8:50 pm | #42 |
Octode
Join Date: Jan 2012
Location: Wimbledon, London, UK.
Posts: 1,465
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Re: RSC Guitar Amplifier.
Here you go. The dark marks are residues from the application of sellotape when the document fell apart yonks ago.
I have included my redrawn circuit diagram, since the original is not too clear in places. I might even be able to find a circuit diagram for my modified amp, with the use of circuit boards, two channels with independent tone-stacks (one with tremolo with speed and intensity) and presence control. When I did this initially, I got a feedback howl on first switch-on which horrified me. It was solved by altering the lead-dress so that two wires were further apart (on the phase-splitter, if I recall correctly). Lead-dress can be very important; what looks like a lovely neat amplifier with wires all in straight lines and laced together, with perfect right-angle bends can be a recipe for an amp with instability problems. If no-one can see it and it works fine, there is little point in being overly tidy. I can only attach the first five pdf files to this message, so I'll have to submit abother one with the rest. Regards, Colin. |
5th May 2012, 8:52 pm | #43 |
Octode
Join Date: Jan 2012
Location: Wimbledon, London, UK.
Posts: 1,465
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Re: RSC Guitar Amplifier.
The rest.
Colin. |
6th May 2012, 9:24 pm | #44 |
Octode
Join Date: Dec 2006
Location: Colchester, Essex, UK.
Posts: 1,076
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Re: RSC Guitar Amplifier.
All the above drawings and circuit are very helpful, thanks Colin, although my amp is a bit different, but certain parts of the circuit follow suit and are very similar.
Anyone got an idea what the grid voltages should be on ECL 82 and ECC 83valves? Mike. |
6th May 2012, 10:26 pm | #45 |
Dekatron
Join Date: Nov 2003
Location: Heckmondwike, West Yorkshire, UK.
Posts: 9,642
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Re: RSC Guitar Amplifier.
Unless they are DC coupled, all first grids should be zero. The grid bias is the cathode voltage, which is positive WRT the grid.
If you can measure anything at the grid it means either a leaky coupling capacitor, or a leaky valve (or valve holder) PS. You probably have this, but the DC voltages are here - http://www.vvttransformers.co.uk/drb...919_chap13.htm Last edited by AC/HL; 6th May 2012 at 10:30 pm. Reason: Afterthought |
7th May 2012, 7:35 am | #46 |
Octode
Join Date: Dec 2006
Location: Colchester, Essex, UK.
Posts: 1,076
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Re: RSC Guitar Amplifier.
Well according to my old wind-up megger, at least two of the electrolitics are reading down to zero, but will have to desolder a few bits first as the megger is probably reading through parallel resistors etc. On one of these caps, the modern digital ohmeter reads 2.6 meg, but vintage megger reads zero !! So it is looking like I will be changing a few caps first, before anything else.
Mike. |
7th May 2012, 8:43 am | #47 |
Rest in Peace
Join Date: May 2011
Location: Preston, Lancashire UK
Posts: 955
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Re: RSC Guitar Amplifier.
Mike, the Megger isn't really suitable for testing electrolytics, use it for wax/paper/polyester types only. Due to the way electrolytics are made, they all exhibit some leakage. Best to test them using an ESR meter as it is the "equivalent series resistance" that is important with electrolytics.
Bill |
15th Jan 2013, 8:00 pm | #48 |
Triode
Join Date: Jun 2007
Location: Portishead, North Somerset, UK.
Posts: 17
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Re: RSC Guitar Amplifier.
I would be grateful for a copy of the Linear amp instructions and schematic, as I have one of these to rebuild.
Thanks |