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  #1  
Old 9th November 2017, 11:41 AM
Aro69 Aro69 is offline
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Default Kit 34 tubes change bias

Hi guys. I'm very happy owner of second hand kit34. I've bought it on Audiojumble two months ago for my Altec speakers. The seller who build this amp gave my also a box of spare tubes. The original 5u4 were changed for different need help to find out what r they. Now I started hear some noise. Not laud but it's hearable... I've swapped tubes back for 5u4 and two ec80 Telefunken for Mullard but noise left. Isn't it from el34? I was also wondering had this amp autobias? It when I change el34 will have to adjust it. If so how to do it?
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  #2  
Old 9th November 2017, 01:03 PM
John Caswell John Caswell is offline
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Default Re: Kit 34 tubes change bias

Hi,
No no need to even think about biassing as the output valves are cathode biassed. All I would suggest is that you buy matched pairs/quads of EL34 as and when.
If you can take a picture of the 5U4 replacement and post her we can have a guess at what it is.
Noise - I would have a look at the resistors in the anode/cathode circuits of the ECF80 as after some time we did find them going noisy/changing in value. R11/12 - 430K, R15/16/19/20 - 100K, R17/18 - 2K2
If they are 1/2 Watt types change them for 1-2 Watt types.
Please report back you findings here.

John

Last edited by John Caswell; 9th November 2017 at 02:49 PM. Reason: Component nrs added
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  #3  
Old 15th November 2017, 02:12 PM
Aro69 Aro69 is offline
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Default Re: Kit 34 tubes change bias

Quote:
Originally Posted by John Caswell View Post
Hi,
No no need to even think about biassing as the output valves are cathode biassed. All I would suggest is that you buy matched pairs/quads of EL34 as and when.
If you can take a picture of the 5U4 replacement and post her we can have a guess at what it is.
Noise - I would have a look at the resistors in the anode/cathode circuits of the ECF80 as after some time we did find them going noisy/changing in value. R11/12 - 430K, R15/16/19/20 - 100K, R17/18 - 2K2
If they are 1/2 Watt types change them for 1-2 Watt types.
Please report back you findings here.

John
Hi John. Thanks for response. I'm not exactly electronic to understand those numbers u wrote. If will have to check some resistors will need more help. I've resize pic with those tubes..
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  #4  
Old 15th November 2017, 02:16 PM
Aro69 Aro69 is offline
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Default Re: Kit 34 tubes change bias

This is that picture.
Attached Images
File Type: jpg IMAG0100-1024x576.jpg (115.7 KB, 45 views)
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  #5  
Old 30th November 2017, 10:59 AM
Aro69 Aro69 is offline
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Default Re: Kit 34 tubes change bias

Hi John. I though well have more problems too measure those resistors, but done it. All resistors keep their values at the level it shoots be. No one is broken. Noise left but must add this noise isn't constant it's gone as time to time and isn't loud the same every time...




Quote:
Originally Posted by John Caswell View Post
Hi,
No no need to even think about biassing as the output valves are cathode biassed. All I would suggest is that you buy matched pairs/quads of EL34 as and when.
If you can take a picture of the 5U4 replacement and post her we can have a guess at what it is.
Noise - I would have a look at the resistors in the anode/cathode circuits of the ECF80 as after some time we did find them going noisy/changing in value. R11/12 - 430K, R15/16/19/20 - 100K, R17/18 - 2K2
If they are 1/2 Watt types change them for 1-2 Watt types.
Please report back you findings here.

John
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  #6  
Old 1st December 2017, 10:39 AM
Richard Richard is offline
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Default Re: Kit 34 tubes change bias

Hi, Is it the integrated version with input switching and a volume control? If so they may be the cause of noise. The input switch in particular can go noisy after a few years or if it was overheated when soldered. Dirty valve pins and sockets can also cause random noise. Is the noise on both channels or just one?
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  #7  
Old 3rd December 2017, 08:46 PM
Aro69 Aro69 is offline
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Default Re: Kit 34 tubes change bias

Hi. This is 100% kit34 build correct with drawings. I've got instruction. It has switch on the back left side. The noise is mainly in right channel. Should I just look for new switch?
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  #8  
Old 4th December 2017, 07:40 AM
bob orbell bob orbell is online now
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Default Re: Kit 34 tubes change bias

Read Richard's post again, you have not answered him correctly, he is not referring to the power switch on the back. BOB
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