[sdiy] Seeking Marshall 1987 guitar amp potentiometers(vintage...1975)

[Travis Shire]

I would not refer to those Sovwreck "5881" tubes as 5881s. They are heavy 
duty replacements for 6L6s and have nothing in common with a real 5881. You 
go and put real 5881s in an amp like that and they won't live long.






>
> This was the standard CTS pot of the day, as sold by RS components. I 
> still
> have 1 NOS 1 Meg Log one it you need it. Sadly, all others are 25K and 
> 50K.
>
> It might be worth putting a pointer knob on a new one and measuring the
> rotation. I seem to remember that the internal stop was made bigger in the
> new design, giving the same rotational angle, which is what counts. I did
> reworked a few of the 50 watt heads for studio use, fitting the now
> unpbtainium Holco low noise resistors, re-doing the heater wiring and
> fitting conductive plastic pots. The 'Marshall Sound' survived intact, but
> with a lot less background noise. Perhaps the most interesting thing I
> discovered at the time was to make sure that the input ECC83's were the
> orginal Mullard 'Long Box' type: (the anode casing is noticably bigger 
> than
> most clones), which made the sound better in a way that is not easy to
> describe but was noticable. You can roll your output valves and bias to 
> your
> own preference.
>
> Oh - and put some decent quality 1K screen feed resistors in whilst you 
> are
> in there - they are famous for either going high in value, or feeding some
> much heat to the solder joint on the valve base that they go open circuit.
> If the EL34 Anodes show a red glowing patch this is the most likely 
> culprit.
> There is a mod issued by Marshall to convert to 5881 output bottles. I 
> have
> the servce bulletin if you want a copy.
>
> Contact me off list about the pot.
>
> Mike
>
>
>
>
>
>
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