Re-tube: How to go about it?

William Williamson · April 2017

I've got a little hiss in the preamp and one of the solutions put forward by the manufacturer was to re-tube it. I figure while I'm there (having had the amp for about 18mo) I may as well do the lot (?).

The Friedman head I have has the following tubes:

Preamp Tubes: 3 x 12AX7
Power Tubes: 2 x EL-84

I spoke to Dave over email and he recommended JJ (originals) or Tungsol (good alternative). Do I just buy these on ebay and then power off the amp, remove the old and in with the new? Are there more reputable sellers? What should I look for?

It looks like this could be costing me on the sharp end of £115, so I want to be correct!

Thanks!

ecc83 · April 2017

I KNOW I am old and meds ridden but I am pretty sure it wasn't THIS dave!

I am not up on current valve prices but I would think £40 pair of 84s? £30-£40 for the 3 pres? P&P fiver? In any case, give ICBM et al more info. Hiss is likely just ONE ECC83!

Dave.

AlasdairDavis · April 2017

Take the ones out of your amplifier and see what they are if you were happy with the way it sounded.

JJ and Tungsol are good alternatives though...

12AX7s are usually called ECC83s in the UK... I believe 12AX7 is an American name for them.

It is a case of take them out and put new ones in. Does your amplifier have a bias control?

webrthomson · April 2017

I'd go to one of the sellers listed in this thread:

http://thefretboard.co.uk/discussion/100714/where-do-you-get-your-tubes-valves

But in terms of what you do yes you just pop them out and replace - if the amps is not fixed bias you will want to find out how to check the bias for the power tubes and make sure it's still in the correct range.

Maynehead · April 2017

Does the hiss come and go? I've had a red plating EL84 in my amp that created a hiss and drop in volume after the amp has been on for a few mins.

Otherwise if it's constant it's most likely a preamp valve, in which case you'd just need to get a new one (Tungsol is a good choice) for about £15, and save yourself a ton.

ICBM · April 2017

I would avoid Tung-Sols if hiss is an issue - they're quite prone to it in my experience. I'm not a fan of JJs tone-wise but at least they don't hiss! (Usually.) TADs are also good, EHs more patchy, Sovteks rather dull-sounding in my opinion. There are many more too, but if the amp came with JJs and you liked the sound of it you may as well stick with them.

As Dave said it's almost certainly just one valve - if it is a valve at all - so don't change all three at once until you've identified which it is that's causing the problem. It's even possible that the same valve which hisses too much in one position can be perfectly OK in another.

I would probably buy one ECC83/12AX7 first, and try it in all three positions. If it doesn't fix the hiss, it's not a valve issue and there's no point in spending money on three new valves - although a single spare is always worthwhile, so you still haven't lost anything at this point.

The EL84s will wear out over time so they could be worth changing anyway, and especially if they *haven't* failed, since that also gives you a known-working spare pair if you keep the old ones. JJs again are probably the best of the modern EL84s, although TADs are good too.

If it's an EL84 amp there's a good chance it's cathode-biased, in which case it's not necessary to bias it - but check, if you can.

William Williamson · April 2017

I can't seem to open that link

@AlasdairDavis there is no control for it, the instructions say it should be returned to retailer for rebiasing. Should I assume anything?

ICBM · April 2017

What model is it? Is there a schematic or a user manual available?

AlasdairDavis · April 2017

William Williamson said:

I can't seem to open that link

@AlasdairDavis there is no control for it, the instructions say it should be returned to retailer for rebiasing. Should I assume anything?

If there isn't one then it'll be fixed biasing so that's one less thing to worry about. Just swap like for like. All those valves should cost you less than £115. Try Watford valves.

jpfamps · April 2017

Firstly I will reiterate, in amp specific threads, PLEASE state which model amp you have. It helps getting good advice.

£115 is a lot for 2 x EL84 and 3 x 12AX7; I would charge less that this for the valves including fitting an any potential bias adjustments (assume you amps needs them).

I'd be looking to pay around £60 retail.

I'd go with JJ EL84s. If the amp is fixed bias then the bias would need adjusting. I can find out whether this is the case BUT WILL NEED TO KNOW THE MODEL OF THE AMP.

Re ECC83s I'm not a huge fan sonically of the regular JJ-ECC83. They tend to be reliable and are reasonably priced, however in amps with lower HT voltages they can make the controls noisy when you turn them due to grid current.

I've not had great results with the Tungsol 12AX7s; they haven't been that reliable and can be noisy.

EH-12AX7s work well, in my opinion, in Fenders, but I would not recommend them in amps with cathode followers (I don't know whether your amp employs a CF, but I can find out).

The latest production Chinese 12AX7 seems fine (at the moment), and the TAD ECC83 is a rebranded Chinese 12AX7.

William Williamson · April 2017

Sorry @jpfamps ;, I should have been more specific! I have a Friedman Runt 20 Head. The 'Dave' mentioned is Dave Friedman.

http://www.ebay.co.uk/itm/JJ-EL84-x-2-ECC83-12AX7-x-3-Premium-Amp-Set-NEW-/220671169555?hash=item336106d413:g:0K4AAOSwdzVXmRM2

It came with JJ's so will it still need adjusting?

@ICBM if I'm just replacing one, then just one of the JJ ECC83's in the interim?

TheBigDipper · April 2017

AlasdairDavis said:

William Williamson said:

I can't seem to open that link

@AlasdairDavis there is no control for it, the instructions say it should be returned to retailer for rebiasing. Should I assume anything?

If there isn't one then it'll be fixed biasing so that's one less thing to worry about. Just swap like for like. All those valves should cost you less than £115. Try Watford valves.

Not sure that's right. I seem to remember that cathode-biased amps do not need you to do anything other than change the valves. They bias themselves. Fixed-bias (confusingly) require you to adjust the bias using a meter once you've changed the valves.

So, no control to set the bias implies cathode-bias, not fixed-bias.

Experts - can I trust my memory?

ICBM · April 2017

William Williamson said:

Sorry @jpfamps ;, I should have been more specific! I have a Friedman Runt 20 Head.

It came with JJ's so will it still need adjusting?

Given that there is no mention whatever in the manual of biasing, although there is of replacing valves, I think it's a reasonable assumption that it's probably cathode-biased. If it's based on the classic Marshall 20W power section it will be.

William Williamson said:

@ICBM if I'm just replacing one, then just one of the JJ ECC83's in the interim?

Yes. The hiss is very unlikely to be anything to do with the power valves anyway.

AlasdairDavis · April 2017

Sorry I meant self bias, I always muddle that up!

William Williamson · April 2017

Well, this is a bit of a dissapointment - I pulled and replaced each preamp tube one by one and replaced with a new JJ ECC83 and there's no difference in sound at all - so I guess it rules that out.

The volume of the noise is about as loud as a person 'huffing' for the hiss, and humming for the... hum.

Any other suggestions? It's not the pedals (going in straight), it's not the FX loop (bypassed), it's not the guitar (no guitar plugged in), and also tried a noise suppressor both in the loop and infront.

ICBM · April 2017

Sounds like a fault with the amp, if it wasn't always like that.

AlasdairDavis · April 2017

TheBigDipper said:

AlasdairDavis said:

William Williamson said:

I can't seem to open that link

@AlasdairDavis there is no control for it, the instructions say it should be returned to retailer for rebiasing. Should I assume anything?

If there isn't one then it'll be fixed biasing so that's one less thing to worry about. Just swap like for like. All those valves should cost you less than £115. Try Watford valves.

Not sure that's right. I seem to remember that cathode-biased amps do not need you to do anything other than change the valves. They bias themselves. Fixed-bias (confusingly) require you to adjust the bias using a meter once you've changed the valves.

So, no control to set the bias implies cathode-bias, not fixed-bias.

Experts - can I trust my memory?

Sorry you're I meant self bias...

AlasdairDavis · April 2017

TheBigDipper said:

AlasdairDavis said:

William Williamson said:

I can't seem to open that link

@AlasdairDavis there is no control for it, the instructions say it should be returned to retailer for rebiasing. Should I assume anything?

If there isn't one then it'll be fixed biasing so that's one less thing to worry about. Just swap like for like. All those valves should cost you less than £115. Try Watford valves.

Not sure that's right. I seem to remember that cathode-biased amps do not need you to do anything other than change the valves. They bias themselves. Fixed-bias (confusingly) require you to adjust the bias using a meter once you've changed the valves.

So, no control to set the bias implies cathode-bias, not fixed-bias.

Experts - can I trust my memory?

Sorry you're I meant self bias...

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Re-tube: How to go about it?

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