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Post subject: Re: Vibrolux Reverb 1968 drip edge bias set-up question
Posted: Sat Oct 12, 2013 3:09 am
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Jimi, not sure what your concern is with the bias adjust pot wiring. But it all looks straight-up, to me. Color code of the wire insulation, seems correct, for a BF circuit. And yeah, Beemer hit on another good point!! Wondering about the tubes. What kind of readings are you getting if the tubes are reversed in the sockets? Art

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Post subject: Re: Vibrolux Reverb 1968 drip edge bias set-up question
Posted: Sat Oct 12, 2013 7:00 am
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jimitrader wrote:
I guess what is concerning me is when i adjust the bias it only balances the bias ? as everyone said it seems to have a BF setup..i did notice on the schematic it has a white wire going to the bias board but on mine it isn't? everything else seems the same to me. :-) but i am still learning.. I am humbled by everyone's smarts..great site right here!!


It is NOT balancing the bias. Far from it. The photo and schematic appear to match. Check the components as suggested (out of circuit) and if they are bad, replace them. Then recheck the tube bias. I bet the tubes are junk also.

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Post subject: Re: Vibrolux Reverb 1968 drip edge bias set-up question
Posted: Sat Oct 12, 2013 10:03 am
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Jimi...
how does the amp sound to you? Do you like it??
If you do then all is good. 5ma between the power tubes is really not that big of a deal.
We all like to see it spot on but I have learned over the years from guys here and on other sites that you can drive yourself nuts trying to get a perfectly matched set and then convincing yourself its sounds better. Not discounting matching tubes or having a healthy PI cicuit just some food for thought.


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Post subject: Re: Vibrolux Reverb 1968 drip edge bias set-up question
Posted: Sat Oct 12, 2013 12:41 pm
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mxvin wrote:
Jimi...
how does the amp sound to you? Do you like it??
If you do then all is good. 5ma between the power tubes is really not that big of a deal.
We all like to see it spot on but I have learned over the years from guys here and on other sites that you can drive yourself nuts trying to get a perfectly matched set and then convincing yourself its sounds better. Not discounting matching tubes or having a healthy PI cicuit just some food for thought.


I suggest you reread the original post.

These are 6L6GCs. The first numbers quoted were 19 and 24 mA, 5 mA apart. Depending on what the plate voltage is, those values are well into crossover distortion territory. Not where you want to bias a set of 6L6GCs. The second set of numbers was 24 and 34 mA. 10 mA apart! That is unacceptable in my book if these tubes were sold as a balanced set. The bias is still too cold for 6L6GCs. No, there is either a problem in the amp or the tubes are junk, or both.

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Post subject: Re: Vibrolux Reverb 1968 drip edge bias set-up question
Posted: Sat Oct 12, 2013 1:18 pm
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bluesky636 wrote:
No, there is either a problem in the amp or the tubes are junk, or both.


+1000

Those tubes should be comfortable at 33-38mA and (if matched, as the seller implied) any differential should be 1.2mA or less.

Just because something sounds pleasing to the ear does not necessarily mean it's healthy for the amp.

Arjay

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Post subject: Re: Vibrolux Reverb 1968 drip edge bias set-up question
Posted: Sat Oct 12, 2013 4:56 pm
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" The second set of numbers was 24 and 34 mA. 10 mA apart! "

If this is all the current you can pull with usual plate voltages of 450-475VDC --- those are definitely tired tubes. Prolly at 50% life. I agree the Bluesky, maybe the OP should try a new set of 6L6GC's, before anything else.


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Post subject: Re: Vibrolux Reverb 1968 drip edge bias set-up question
Posted: Sat Oct 12, 2013 5:57 pm
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BMW2002Ti wrote:
" The second set of numbers was 24 and 34 mA. 10 mA apart! "

If this is all the current you can pull with usual plate voltages of 450-475VDC --- those are definitely tired tubes. Prolly at 50% life. I agree the Bluesky, maybe the OP should try a new set of 6L6GC's, before anything else.


Agree, but according to jimi:

jimitrader wrote:
I ordered these tubes from Gerald Weber website..they where supposed to be NOS but he sent jj tubes 6l6gc ?I have played maybe two hours on them total? is there a way to set the amp up with true idle-bias?

:shock:

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Post subject: Re: Vibrolux Reverb 1968 drip edge bias set-up question
Posted: Sat Oct 12, 2013 6:05 pm
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Hmm... I'd try another set of 6L6GC and see what values I get. "NOS" a very loose term these days. Kinda like: "You'll like my sister, she's a virgin." :lol:


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Post subject: Re: Vibrolux Reverb 1968 drip edge bias set-up question
Posted: Sat Oct 12, 2013 6:12 pm
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bluesky636 wrote:
mxvin wrote:
Jimi...
how does the amp sound to you? Do you like it??
If you do then all is good. 5ma between the power tubes is really not that big of a deal.
We all like to see it spot on but I have learned over the years from guys here and on other sites that you can drive yourself nuts trying to get a perfectly matched set and then convincing yourself its sounds better. Not discounting matching tubes or having a healthy PI cicuit just some food for thought.


I suggest you reread the original post.

These are 6L6GCs. The first numbers quoted were 19 and 24 mA, 5 mA apart. Depending on what the plate voltage is, those values are well into crossover distortion territory. Not where you want to bias a set of 6L6GCs. The second set of numbers was 24 and 34 mA. 10 mA apart! That is unacceptable in my book if these tubes were sold as a balanced set. The bias is still too cold for 6L6GCs. No, there is either a problem in the amp or the tubes are junk, or both.


I didnt see the 10mA difference and you are right the bias even at 19 and 24 is way cold. I should have realized that.
carry on...:)


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Post subject: Re: Vibrolux Reverb 1968 drip edge bias set-up question
Posted: Sat Oct 12, 2013 8:17 pm
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Hello ..i just got done replacing the 2 original 220k resistors as mentioned earlier with 2x 220k ohm 1/2 watt 5% resistors...i also replaced a resistor at the input jack to 1M 1/2 watt 5% because the one there was wrong according to the schematic...now i got a reading of 25.8 and 20.8 and it will only balance not adjust?..also now my reverb is very faint if even there at all..if i crank the rev all the way and bang the tank i get the spring noise coming through the speakers..what do you suppose went wrong?

just checked it with a GZ34 and 2 GT 6l6GE tubes from my super rev...now the readings are 35.6 and 36.6 MA and it sounds way better..but still a problem with the rev? is it possible for some solder to spread underneath the turret board and cause this? or maybe its a coincidence and my rev unit is going bad? i also traded the 4th pre amp tube just after the rev transformer to see if maybe that was it but no luck...


ok back again...it was a coincidence the connection wire on the tank frayed loose? soldered back and now i am finally able to sit here and play the amp it sounds awesome now!!!
so to re-cap for anyone else going through the same project:

Changed the 2 bias 220k resistors (they had strayed way off 220k) - ( 240k )
Changed input jack resistor to 1M 1/2 watt 5%
Changed the power tubes to GZ34 GT 6l6 GE ..(35 MA now)
Fixed reverb cord ...Thanks everyone who helped on this project!! :D


Last edited by jimitrader on Sat Oct 12, 2013 9:15 pm, edited 1 time in total.

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Post subject: Re: Vibrolux Reverb 1968 drip edge bias set-up question
Posted: Sat Oct 12, 2013 8:54 pm
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jimitrader wrote:
Hello ..i just got done replacing the 2 original 220k resistors as mentioned earlier with 2x 220k ohm 1/2 watt 5% resistors...i also replaced a resistor at the input jack to 1M 1/2 watt 5% because the one there was wrong according to the schematic...now i got a reading of 25.8 and 20.8 and it will only balance not adjust?..also now my reverb is very faint if even there at all..if i crank the rev all the way and bang the tank i get the spring noise coming through the speakers..what do you suppose went wrong?

just checked it with a GZ34 and 2 GT 6l6GE tubes from my super rev...now the readings are 35.6 and 36.6 MA and it sounds way better..but still a problem with the rev? is it possible for some solder to spread underneath the turret board and cause this? or maybe its a coincidence and my rev unit is going bad? i also traded the 4th pre amp tube just after the rev transformer to see if maybe that was it but no luck...


So clearly the tubes you got from Kendrick Amps are faulty. Hopefully they will take them back and sent you a set of properly balanced tubes. If you want JJs, get them from Eurotubes (http://www.eurotubes.com/). I buy all my JJs from them and they are all very well balanced.

You replaced the reverb receiver tube (should be a 12AX7). You probably need to replace V3, the reverb driver tube which is a 12AT7.

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Post subject: Re: Vibrolux Reverb 1968 drip edge bias set-up question
Posted: Sat Oct 12, 2013 9:24 pm
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Gerald Weber refused to honor the transaction on his site...i actually paid for NOS rare tubes at a higher price than normal and was sent these? they said they ran out and sent next best thing? so i asked for a small refund for the difference and he said o it is my daughters fault? can't do it? so anyway after going around and around on email..i gave up and filed a claim on the better business bureau site and he got real mad and called here and left me a big ole nasty message chewin me out about how great he is and how could i do that? :lol: whatever...he sure makes good amps though!!!:-) but it looks like all 3 tube are weak..I will try euro-tubes!! thanks...J


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Post subject: Re: Vibrolux Reverb 1968 drip edge bias set-up question
Posted: Sat Oct 12, 2013 9:34 pm
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I've never trusted that clown......not his tubes, not his books, not his advice.

Arjay

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Post subject: Re: Vibrolux Reverb 1968 drip edge bias set-up question
Posted: Sat Oct 12, 2013 10:11 pm
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I have never had a problem dealing with the guys at Eurotubes. I have e-mailed them with questions and they respond within 24 hours. They send an e-mail when they receive the order and one when they ship. Often I send an e-mail when the tubes arrive and after I try them out. They always respond. They provide a 6 month warranty on all their tubes.

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Post subject: Re: Vibrolux Reverb 1968 drip edge bias set-up question
Posted: Sat Oct 12, 2013 10:53 pm
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+1

I've ordered from Eurotubes many times though never stuff for my own amps. They always send exactly what I order and they strike me as very courteous and conscientious about their business.

Arjay

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