'72 SB restore: Can I use 0.022uF/160V NOS Mustard caps in the preamp section?

Carl M

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I am restoring a '72 Super Bass which has had its preamp replaced by a preamp on a separate board by a previous owner. Apart from the preamp section which was empty except for the turrets, the rest of the amp was untouched when I bought it, except for the presence control and the ware-out-parts like the tubes and some caps in the PSU.

I managed to source some 0.022uF/160V NOS Mustard caps, but the question is will they be safe to use in the preamp section of an old SB? Or do I need to replace them with higher voltage Mustard caps which are more challenging to source.

The amp is now up and running with the restored preamp and the 0.022uF/160V caps fitted. The only thing left to do is to change the presence pot and its cap. (Which are working fine, but not true to 1972 specs) But the amp sounds great along with the matching '71/'72 1982A/B cabs, however I need to be sure that the 160V caps in the preamp are safe to use for long term use.

Does anyone here know...?
 

Spanngitter

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You did restore the PreAmp but not take any measurements what Voltages are present around the caps?
For the surroundings of V1 you might be below Spec on the 160V barely but for any other point in the Amp you are most likely exceeding by far.
Since it is a rebuild and not a restore of a collectors item what does speak against equipping it with proper NP Vishay/Roedersteins MKT1813?
 

neikeel

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I’ve seen them fitted ex-factory, although it would make me nervous I suspect that they are pretty robust with wide voltage handling range.
Anyone know for sure?
 

South Park

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If you want to use them for coupler caps not high enough voltage rating . You want a rating equal to the b voltage . You can use them on the lower voltage stuff .
 

StingRay85

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To be honest, I would swap them out just to be on the safe side. That amp is too valuable to save out a few bucks for not replacing something that works "now", but could cause failures in the near future.
 

Pete Farrington

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If the valve fails, the voltage on the cap will most probably rise, possibly up to the HT node voltage, eg >300VDC.
So it really doesn’t seem to be a good idea.
 

Carl M

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You did restore the PreAmp but not take any measurements what Voltages are present around the caps?
For the surroundings of V1 you might be below Spec on the 160V barely but for any other point in the Amp you are most likely exceeding by far.
Since it is a rebuild and not a restore of a collectors item what does speak against equipping it with proper NP Vishay/Roedersteins MKT1813?

Thank you for the response.

To cut a long story short, I wanted to buy a 1972 1982B cab for my 1971 1982A cab, but the owner would only sell the cab together with this 1972 Super Bass which was in great condition except for the replaced preamp.

I didn't need the head because I already had my 1976 Super Lead and a home made '67 spec Lead 50 (1987) head, but I really wanted this cab and I had been chasing one for a long time so I agreed to the deal.

The amp was in good condition but the added preamp made it sound like an 80's metal amp and since it was a relatively easy job to remove the added Mesa/Fender inspired preamp board and replace the missing caps and resistors in the original preamp, I sourced some NOS Mustard caps and we started rebuilding it.

You are absolutely right. We should have measured all voltages, but we didn't. The amp had recently been serviced re-tubed by a qualified technician (actually one of the previous owners of the amp) before I bought so I knew that the power amp and the PSU worked as they should and then I felt that the voltages feeding V1 and V2 should be fine. But then again, I know, I know, I should have checked all voltages in the preamp... :)

Then I just realized that all Super Bass and Super Lead kit seemed to contain 400V caps in the preamp and then I thought that I should ask which voltage the preamp caps needed to be rated at.

If I need to replace the 160V caps I will probably drop the idea of restoring it with NOS Mustard and instead convert the rebuilt preamp to Super Lead spec using new caps like Sozos or similar while keeping the rest of the amp as it is, because I would have more use of an amp with a brighter and a darker channel which I can run in parallel like a Super Lead than a Super Bass with its two similar "Normal" channels.

But then another alternative would be to restore it to original spec and sell it to someone else who really wanted and appreciated a vintage turret board Super Bass or trade it for a vintage Lead 50 (1987) which I would have more use for.

You say that the 160V caps would be fine around V1, but what about the two around V2?
 

Carl M

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To be honest, I would swap them out just to be on the safe side. That amp is too valuable to save out a few bucks for not replacing something that works "now", but could cause failures in the near future.

OK. Then keeping them is not an alternative. Then I just need to see if I can source some higher voltage Philips/Mullard Mustards. Otherwise I need to decide if I should do a partial conversion to Super Lead or just use new caps to wire it to Super Bass 1972 specs.

Many thanks to everyone for the input!
 
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StingRay85

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Original Philips 400V 22nF can still be easily found, although not cheap either. Where are you located?
 

Carl M

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Original Philips 400V 22nF can still be easily found, although not cheap either. Where are you located?

I live in Sweden, so I prefer to to source components in the EU (and possibly UK unless it's high value items which I need to pay 25% VAT plus customs declaration fees for).
 

StingRay85

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There seems to be a guy in Germany selling them on Reverb. You probably won't find them any cheaper than 15 € a piece. I would contact him and try to make a deal with him outside of Reverb.
 

Carl M

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There seems to be a guy in Germany selling them on Reverb. You probably won't find them any cheaper than 15 € a piece. I would contact him and try to make a deal with him outside of Reverb.

Thanks. The price is fine considering the kind of amp I am working on. I just need to decide which way I should go, swapping the caps and keeping it original Super Bass spec or convert the preamp to Super Lead spec and keep it forever... :)
 

StingRay85

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I also have a stock of 2000+ new mustard caps, in case you can't find what you need, but I prefer to save those for restorations in the coming decades when they become more difficult to find.
 

neikeel

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If you set it up properly as a Superlead you will probably find that the channel 1 is bright and in your face ie normal SL and the channel 2 is like the earlier SL or later SB. To get ‘the tones’ the volume pot on either channel needs to be over 7 on the dial.
 

Carl M

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If you set it up properly as a Superlead you will probably find that the channel 1 is bright and in your face ie normal SL and the channel 2 is like the earlier SL or later SB. To get ‘the tones’ the volume pot on either channel needs to be over 7 on the dial.

I have owned '76 Super Lead since I was 18 and also have a Lead 50 (1987) and a Studio Vintage 20H, so I am quite familiar with the Super Lead's control. I always jump the channels and and balance them to get the sound and response I like. I owned a '67 Super PA which I sold to get the SL and I have always missed the magic of those really old heads and that's why I am consider converting my '71 SB's preamp to SL spec to get a really old Marshall with a bright and a normal channel which I can combine to nail my favourite Marshall tones. But we'll see, I haven't decided yet.
 
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