vintage 1967 deluxe reverb filter caps?

[ampdan]

..

[echo44]

Wow, so I changed the power supply caps and bias cap,
I am not sure if its my imagination but my amp sounds at least twice
as loud Everything feels tighter. Cant believe I waited so long to do this.
What a no brainer!!

[jelle]

Don't forget your cathode caps....

[echo44]

that will be my next job have to order some more caps.
just curious what happens if you use cap rated at higher voltage thn need but the correct capacitance value. Don't plan to do this but have always been curious about this

[echo44]

I biased the amp to -35v as per the suggestion on this video
Is that the correct value?
http://www.youtube.com/watch?v=p3dEY9FcSuo
Thanks

[rdjones]

can i use a 25uF 50V instead of the 50uF 50 volt as that is all I have
and out of curiosity if the schematic calls for a 25/50 why is there a 50/50?
It looks original?

50 uF is correct, it's a running change.
The 1968 schematic was changed to show the updated value.

reddog Steve

[rdjones]

I biased the amp to -35v as per the suggestion on this video
Is that the correct value?
http://www.youtube.com/watch?v=p3dEY9FcSuo
Thanks

Yes, -35V is the bias voltage shown on several schematics.

Unless you want to use the more technical and accurate method of measuring idle current and adjusting to a particular % of dissipation.
Me, I'd just set it to -35 and turn it loose.

regards,
rd

[xtian]

You can use caps spec'd for higher voltage with no drawbacks other than cost and size.

[JazzGuitarGimp]

You can use caps spec'd for higher voltage with no drawbacks other than cost and size.

+1 on that. 10-4 good buddy!

[martin manning]

Me, I'd just set it to -35 and turn it loose.

I wouldn't have thought there is enough consistency among tubes to do that... Am I wrong?

[jelle]

I would say you are considerate or careful in how you phrase things.

There is not enough consistency between both tubes and power transformers to do it this way is a safe and reproducible manner. The only consistent way is to measure the current itself. And frankly it is just as much work.

This is an excellent text on the topic:
http://www.duncanamps.com/technical/lvbias.html
This is a GREAT tube vendor if I may add.

I hope I did not sound like an ass, this topic keeps coming up and stems from a time when Fender used consistent tubes with their Schumacher transformers. Nowadays, the tubes are less consistent, and we use all kinds of transformers, adding variability, and so the old ways are no longer the best idea. Hope this helps. Jelle

[rdjones]

Me, I'd just set it to -35 and turn it loose.

I wouldn't have thought there is enough consistency among tubes to do that... Am I wrong?

Tubes that don't operate properly at specified circuit parameters are "bad" (using the good/bad scale).
That's not to say they can't be used with an adjustment.

I guess if you're using current production replacements then, no, there's probably not enough consistency to restore a '60s amp to it's heyday glory with just a simple bias voltage check/setting.
But original tubes and their contemporary replacements were more consistent.
Back in the day we didn't have bias probes or worry about minor differences in idle current.
As long as a tube wasn't redplating and it produced sound it was considered working.

Oh, to dream of a simpler day ...

rd

[jelle]

Agreed.

[rdjones]

I hope I did not sound like an ass, this topic keeps coming up and stems from a time ...

I thought that was my job, but I know I can count on you guys to call me out when I make vague blanket statements that might be misinterpreted.


rd

[jelle]

Haha, yeah.

Most of us know all this already. I wrote this to prevent someone with less experience mess up their amp because of something they read here. Sometimes a little bit of knowledge is a dangerous thing.