Concordant Exhilirant pre-amp capacitors

tankertop

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Got one of the above opened up as I'm plumbing in a replacement transformer. Was thinking about replacing the two main power supply capacitors but they are unmarked aluminium cans. Anybody familiar with the design who might have a clue as to their value/rating?

 

Valvebloke

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The collective experience with Doug Dunlop's (Doug was Concordant) modified Quad IIs is that there are hardly two that are the same. He was an experimenter/developer and he changed this and that from unit to unit. The Exhilarant was more like a production piece, so there may be more consistency in those. But I still wouldn't be surprised to find a range of different values for the reservoir and smoothing caps. For what it's worth, Doug tended to use solid-state rectifiers in his Quad IIs. There was often a large bottle in what had been the rectifier socket. But this was simply used to control the current through the smoothing choke and was delayed by the warm-up time of the valve's heater. This avoided the application of a damagingly high electric field to the KT66 cathodes before they'd had a chance to reach operating temperature which, obviously, is a feature of SS rectification.

VB

 

awkwardbydesign

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I was given this circuit for the Concordant Excelsior, ECC81 or ECC82(12AU7). Don't know if it will help.

http://oldstockaudio.blogspot.co.uk/2010/02/www.oldstockaudio.com

12AU7 / 12BH7 / 6CG7: What's best?

The 12AU7, 12BH7, and 6CG7 have very similar electrical characteristics and can usually be substituted for each other. When deciding what's best for you, the following notes may be helpful:

(1) A 12AU7 is identical to a 6CG7 electrically and in the circuit it will function identically. However, there is a different heater pin out. So if you are substituting you need to make a change. In addition, the 6CG7 draws twice as much heater current so be sure that this will work in your circuit. (This may be one reason it is not as popular as it should be.)

 

awkwardbydesign

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I'm no expert, (not even close!), coco or Valvebloke would be better, but I can't see a bridge rectifier here, and if the 6CG7 IS rectifiying, then 220mF each cap? One per valve. A guess only.

 

i_should_coco

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I'm no expert, (not even close!), coco or Valvebloke would be better, but I can't see a bridge rectifier here, and if the 6CG7 IS rectifiying, then 220mF each cap? One per valve. A guess only.
That's because the power supply is missing in action. Can you see a transformer?

 

awkwardbydesign

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That's because the power supply is missing in action. Can you see a transformer?
No, but I can see lots of bare wires which MIGHT have been from the transformer; short of tracing the whole circuit on paper and asking for all the resistor values, it was as I said a guess. Now seeing that there was a bridge, it changes things. So, over to the experts-

 

tankertop

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All words of wisdom gratefully received. Was also wondering whether replacing the quad of 1.5ufs with a pair of 3ufs would cause any performance losses?

 

Valvebloke

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Any thoughts Wammers? Itching to get this back into service...
To be honest the values are unlikely to be very critical. I haven't traced the circuit but it looks as though each channel has a regulator after the smoothing caps and that ought to take out any residual hum if the caps are on the small side. Pre's only draw relatively low current so there's no real reason for the psu ripple to be excessive in the first place. And I think the Exhilarant is a line level unit isn't it ? If it is then it won't be particularly noise-sensitive either. If you were to make the caps absolutely enormous then you could in principle induce high-current switching noise from the solid state rectifier. But there's no need to do that. There's a pic here http://www.flickr.com/photos/bellaphon/6158067169/in/photostream/ which shows they're 400V rated, but I can't read the capacitance values. I'd have thought 100uF would have been plenty and the 220uF shown in awkwardbydesign's circuit plenty plenty. Just a guess though. As Pete says, a meter should give you a near enough value pretty quickly.

VB

 

tankertop

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Ok, many thanks. And yes, it's line level only. Have posted a question to the chap who had the Exhiliarant for sale, on the offchance he snapped it from the other angle.

To be honest the values are unlikely to be very critical. I haven't traced the circuit but it looks as though each channel has a regulator after the smoothing caps and that ought to take out any residual hum if the caps are on the small side. Pre's only draw relatively low current so there's no real reason for the psu ripple to be excessive in the first place. And I think the Exhilarant is a line level unit isn't it ? If it is then it won't be particularly noise-sensitive either. If you were to make the caps absolutely enormous then you could in principle induce high-current switching noise from the solid state rectifier. But there's no need to do that. There's a pic here http://www.flickr.com/photos/bellaphon/6158067169/in/photostream/ which shows they're 400V rated, but I can't read the capacitance values. I'd have thought 100uF would have been plenty and the 220uF shown in awkwardbydesign's circuit plenty plenty. Just a guess though. As Pete says, a meter should give you a near enough value pretty quickly.VB
- - - Updated - - -

My DMM quite limited in that regards, does very small values only...

Can you measure the values?
 

tankertop

Wammer
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Jan 29, 2009
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We have an answer. Dropped a line yesterday to Walrus who are selling one of these. Pete from the shop kindly looked inside theirs and informs me that the caps in question are 220uf/400v. Kudos to that man!

 

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