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Post subject: 68 Custom Vibrolux hiss
Posted: Wed May 09, 2018 6:19 am
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I've had my 68 Custom Vibrolux from new (about 3 years). It's been good as gold but recently I discovered a hiss.

The hiss is constant - it doesn't increase or decrease with the turning of the knobs and it's present even when there is nothing plugged in the amp. Plugging a cable makes no difference (better or worse), so the source of the hiss is in the amp itself.

I've tried disconnecting the speakers, one by one, then swapping the power valves with two new ones. Nothing changes. I guess this would not be an issue at stage volume (like I said, it does not increase with the volume turned up), but it's a nuisance and frankly a distraction when I practice quietly at home. It will also be a problem when recording.

Any thoughts / suggestions / guesses as to the source of the hiss and the possible remedy?
Thanks


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Post subject: Re: 68 Custom Vibrolux hiss
Posted: Wed May 09, 2018 8:18 am
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The phase inverter tube next to the power tubes is probably the culprit.


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Post subject: Re: 68 Custom Vibrolux hiss
Posted: Wed May 09, 2018 8:52 am
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TimsAudio wrote:
The phase inverter tube next to the power tubes is probably the culprit.


Do you mean the 12AT7? There are two of them and I swapped them round but nothing changed.


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Post subject: Re: 68 Custom Vibrolux hiss
Posted: Wed May 09, 2018 9:38 am
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tremolo arm wrote:
TimsAudio wrote:
The phase inverter tube next to the power tubes is probably the culprit.


Do you mean the 12AT7? There are two of them and I swapped them round but nothing changed.



Yes one for the reverb and one for the phase inverter.

A noisy 12AX7 ?


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Post subject: Re: 68 Custom Vibrolux hiss
Posted: Wed May 09, 2018 9:49 am
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stratele52 wrote:
tremolo arm wrote:
TimsAudio wrote:
The phase inverter tube next to the power tubes is probably the culprit.


Do you mean the 12AT7? There are two of them and I swapped them round but nothing changed.



Yes one for the reverb and one for the phase inverter.

A noisy 12AX7 ?


Like I said, I swapped them, but the issue is still there. Should I just take each out, one at the time and see what happens? That's not likely to do any damage, right?


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Post subject: Re: 68 Custom Vibrolux hiss
Posted: Wed May 09, 2018 12:00 pm
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Power amp OFF, remove V1 a 12 AX7
Power ON hiss or not ?
No hiss; replace V1 with a know good tube
Hiss ; leave V1 unplug

Do same with V2 , V3, V4, V5, V6

Report

It is safe to run the amp with no 12XX7 on it or no 6L6


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Post subject: Re: 68 Custom Vibrolux hiss
Posted: Wed May 09, 2018 12:48 pm
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I think I found the culprit - it's a 12AX7 (in this case the original Groove Tubes ECC83-S) in position V3. Swapped that with a ECC83-S from V5 and the noise was gone.

I don't have any 12AX7's hanging around. Which brand / type would you recommend that I buy to match the rest (which are all Groove Tubes)? I am in the UK?

Thanks


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Post subject: Re: 68 Custom Vibrolux hiss
Posted: Wed May 09, 2018 1:51 pm
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tremolo arm wrote:
I think I found the culprit - it's a 12AX7 (in this case the original Groove Tubes ECC83-S) in position V3. Swapped that with a ECC83-S from V5 and the noise was gone.

I don't have any 12AX7's hanging around. Which brand / type would you recommend that I buy to match the rest (which are all Groove Tubes)? I am in the UK?

Thanks


A new 12AX7 don't need to be matched. Best is to mix many brands on 12XX7 tubes.

Mixing several brands of 12XX7 helps to reduce defects and increase the qualities of each brand.

Groove Tube don't built tubes, they rebrand tube made by Sovtek and JJ and other

JJ ECC83 is a good tube
Tung sol is good too, I like more than JJ

http://www.thetubestore.com/Tubes/Groove-Tubes

Image[url=https://flic.kr/p/25U9zx1]


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Post subject: Re: 68 Custom Vibrolux hiss
Posted: Wed May 09, 2018 1:58 pm
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tremolo arm wrote:
I think I found the culprit - it's a 12AX7 (in this case the original Groove Tubes ECC83-S) in position V3. Swapped that with a ECC83-S from V5 and the noise was gone.

I don't have any 12AX7's hanging around. Which brand / type would you recommend that I buy to match the rest (which are all Groove Tubes)? I am in the UK?

Thanks


If amp play well at every channel with reverb and /or tremolo ( V5) you can leave this tube there. No need to buy a new tube.


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Post subject: Re: 68 Custom Vibrolux hiss
Posted: Wed May 09, 2018 4:43 pm
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I had the exact problem with my 65 TRRI right out of the box. I replaced the offending 12AX7 as well as the other 12AX7's with Tung-Sol's (Russian made) and the amp sounds phenomenal. It's so quiet, I'm not sure it's on until I play something. These are easily available in the US, but not sure about overseas.


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Post subject: Re: 68 Custom Vibrolux hiss
Posted: Thu May 10, 2018 1:08 am
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LawFlow wrote:
I had the exact problem with my 65 TRRI right out of the box. I replaced the offending 12AX7 as well as the other 12AX7's with Tung-Sol's (Russian made) and the amp sounds phenomenal. It's so quiet, I'm not sure it's on until I play something. These are easily available in the US, but not sure about overseas.


Available at Tube amp Doctor at 16.40 Euros.

http://www.tubeampdoctor.com/en/shop_Ot ... Sol_Tubes/

or
https://www.thomann.de/gb/tung_sol_12ax ... arch_prv_9


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