Fender HRD Volume Drop & Very Blue Valves

gubble

Took my Fender HRD to rehearsal last night (after the previously mentioned debacle regarding the provided amps).

At the end of the evening I noticed the amp was starting to get quieter. Looking round the back I also noticed the valves were very blue and hazy (one more so than the other) - looked pretty but I'm sure I've heard somewhere that this could indicate they are worn.

Obviously I can't get a 100% diagnosis without someone seeing the amp but is this sounding like it needs a new pair of valves for the power amp?

If so which ones do I need as there seems to be so many 6L6 variants and also would I need to re-bias the amp if I pop in a matched pair?

I've been very blessed with valve amps for the years I've used them and not yet had to replace any valves. I purchased this second hand over a year ago and it's done probably over 50 gigs since I've owned it so i'ove no idea how old the valves actually are in it or how much use they've had.

ICBM

Blue glow is almost always NOT a sign of valve problems. It's about the most persistent and wrong valve myth there is.

Almost all power valves glow slightly blue *when they're working properly* - some more than others. If there's no blue glow at all, chances are the valve is either dead or biased so cold it's effectively turned off.

That said you can't necessarily tell that they're OK from it either. If the blue glow is too intense the valves could be biased too hot, but in that case you will usually see 'redplating' - the grey pate structure glowing red-hot, often along the seams. If that's the case the amp will often start to lose power after it's been on a while.

Fender amps sold in this country often have a problem with running too hot because they are set for 230V as per EU regulations - but the supply here is still really 240V, and sometimes higher. You can fix this easily by moving two push-connectors on the PCB.

It would be worth buying a new set of power valves anyway though if the existing ones are more than a couple of years old and have been used a fair amount - even if it turns out not to be the valves, spares are always a good idea. If it does turn out to be them, keep the old ones since you know they actually work enough to get you through an emergency if one of the new ones fails. (They can - don't assume that they won't just because they're new.)

Any standard 6L6s will be fine, JJs seem reliable and are good value for money. I get them from Karltone. It would also be worth buying at least one spare 12AX7 for the same reason - you can use it to see if any of the existing valves are weak, and if not then it's useful as a spare - and some F1.6A fuses, which you will need if it ever does blow a power valve.

gubble

Thank You @ICBM going to get a pair ordered today. I've a spare 12AX7 somewhere that I bought as a spare.

Any ideas what might have caused the volume drop?

impmann

When I was gigging my HRD, I swapped the original Groove Tubes out for a pair of Ruby Tubes (shit, they were horrid) and a set of JJs (not bad, but sounded different to how it sounded previously). I then chucked in a set of new Groove Tubes and to my ears, it sounded happier and more like the sound I liked when I bought it. Each time, the valves were biased  - its easy to do with a mutimeter on a HRD. I forget the factory settings, but thats what I aimed for.

In terms of volume drop... can't help, sorry.

Good luck

ICBM

gubble said:

Any ideas what might have caused the volume drop?

If it was slow and over a period of high-volume use then the power valves are still the most likely.

If it was sudden then it could be a valve (any of them), or a failed resistor in the phase inverter circuit which is quite a common fault on these - but that produces an oddly dirty sound as well as a volume drop.

gubble

Thanks for the responses guys.

As I'm just about to enter a very busy period of gigs I thought it best that I drop it into my local tech to solve the problem and make sure everything is in tip top working order

Funkfingers

For over a decade, Fender has had a tie-in with Groove Tubes. Replacing one duet of Fender/Groove Tubes 6L6s for another of the same (alleged) rating is the easiest way to avoid rebiassing issues. 

I live in the back of beyond. There are few stockists. I mail order from Watford Valves.

crunchman

impmann said:

When I was gigging my HRD, I swapped the original Groove Tubes out for a pair of Ruby Tubes (shit, they were horrid) and a set of JJs (not bad, but sounded different to how it sounded previously). I then chucked in a set of new Groove Tubes and to my ears, it sounded happier and more like the sound I liked when I bought it. Each time, the valves were biased  - its easy to do with a mutimeter on a HRD. I forget the factory settings, but thats what I aimed for.

In terms of volume drop... can't help, sorry.

Good luck

Factory settings are actually quite cold.  If you like them then fine, but you can go a bit higher if you want - or you can use it as a safety net against higher mains voltage.  There is plenty on the internet to tell you what the settings are.

It does depend on your mains voltage, as @ICBM says.  When I had a HRD I measured 456V on the plates of the power valves.  The schematic says 430V.  I then measured the incoming AC on the power transformer at 246V which would account for the difference.  As the factory settings are quite cold, you should be ok with a Hot Rod Deluxe even if the mains voltage is a bit high.  Not sure about something like the Hot Rod DeVille that is a very similar circuit but pushes the valves harder - a quick google suggests an official 471V on the plates of the Hot Rod DeVille.

jpfamps

crunchman said:

impmann said:

When I was gigging my HRD, I swapped the original Groove Tubes out for a pair of Ruby Tubes (shit, they were horrid) and a set of JJs (not bad, but sounded different to how it sounded previously). I then chucked in a set of new Groove Tubes and to my ears, it sounded happier and more like the sound I liked when I bought it. Each time, the valves were biased  - its easy to do with a mutimeter on a HRD. I forget the factory settings, but thats what I aimed for.

In terms of volume drop... can't help, sorry.

Good luck

Factory settings are actually quite cold.  If you like them then fine, but you can go a bit higher if you want - or you can use it as a safety net against higher mains voltage.  There is plenty on the internet to tell you what the settings are.

It does depend on your mains voltage, as @ICBM says.  When I had a HRD I measured 456V on the plates of the power valves.  The schematic says 430V.  I then measured the incoming AC on the power transformer at 246V which would account for the difference.  As the factory settings are quite cold, you should be ok with a Hot Rod Deluxe even if the mains voltage is a bit high.  Not sure about something like the Hot Rod DeVille that is a very similar circuit but pushes the valves harder - a quick google suggests an official 471V on the plates of the Hot Rod DeVille.

I assume you didn't have your amp wired for 240V mains rather than 230 V mains.

This would account for the difference.

246 VAC is only 2.5% above 240.

jpfamps

Funkfingers said:

For over a decade, Fender has had a tie-in with Groove Tubes. Replacing one duet of Fender/Groove Tubes 6L6s for another of the same (alleged) rating is the easiest way to avoid rebiassing issues. 

I live in the back of beyond. There are few stockists. I mail order from Watford Valves.

Fender actually own Groove Tubes.

crunchman

jpfamps said:

crunchman said:

impmann said:

When I was gigging my HRD, I swapped the original Groove Tubes out for a pair of Ruby Tubes (shit, they were horrid) and a set of JJs (not bad, but sounded different to how it sounded previously). I then chucked in a set of new Groove Tubes and to my ears, it sounded happier and more like the sound I liked when I bought it. Each time, the valves were biased  - its easy to do with a mutimeter on a HRD. I forget the factory settings, but thats what I aimed for.

In terms of volume drop... can't help, sorry.

Good luck

Factory settings are actually quite cold.  If you like them then fine, but you can go a bit higher if you want - or you can use it as a safety net against higher mains voltage.  There is plenty on the internet to tell you what the settings are.

It does depend on your mains voltage, as @ICBM says.  When I had a HRD I measured 456V on the plates of the power valves.  The schematic says 430V.  I then measured the incoming AC on the power transformer at 246V which would account for the difference.  As the factory settings are quite cold, you should be ok with a Hot Rod Deluxe even if the mains voltage is a bit high.  Not sure about something like the Hot Rod DeVille that is a very similar circuit but pushes the valves harder - a quick google suggests an official 471V on the plates of the Hot Rod DeVille.

I assume you didn't have your amp wired for 240V mains rather than 230 V mains.

This would account for the difference.

246 VAC is only 2.5% above 240.

It was stock so wired for 230V.  It had the range to bias it without any problems.   I guess the preamp valves would have been running at slightly higher voltage than the schematic gave as well, but it didn't seem to chew them up.

ICBM

crunchman said:

It does depend on your mains voltage, as @ICBM says.  When I had a HRD I measured 456V on the plates of the power valves.  The schematic says 430V.  I then measured the incoming AC on the power transformer at 246V which would account for the difference.  As the factory settings are quite cold, you should be ok with a Hot Rod Deluxe even if the mains voltage is a bit high.  Not sure about something like the Hot Rod DeVille that is a very similar circuit but pushes the valves harder - a quick google suggests an official 471V on the plates of the Hot Rod DeVille.

Yes, it's a more serious issue on the Deville. The schematic says 485V, but they will usually run at over 500V with UK mains voltage when wired for 230V, which is getting a bit high for modern 6L6s.

Another problem with both amps is the *low* voltage supply - because it's regulated with 16V Zener diodes, this stays fixed whatever the supply voltage... but that means that when the supply voltage is too high, the 470-ohm drop resistors have to get rid of all the extra, which puts a disproportionately higher voltage on them, and hence higher power dissipation.

DJH83004

One of the classic problems with the harmonised UK standard mains voltage, it is 230v +10v, - 6v, so by following the directive, manufacturers will set the voltage tap at 230v, but as we all know it is 240v in the UK and tends to rise above that in many areas.  

ICBM

DJH83004 said:

One of the classic problems with the harmonised UK standard mains voltage, it is 230v +10v, - 6v, so by following the directive, manufacturers will set the voltage tap at 230v, but as we all know it is 240v in the UK and tends to rise above that in many areas.  

It can be over 250V where I work in central Glasgow. I've even measured it at over the 253V limit, although my meter is not super accurate… but the same meter gives 235-240V at home, so it won't be far off. As you can imagine this can be fairly hard on amps.

230V is a classic Euro-fudge, but sadly abandoning it will not be one of the 'benefits' of Brexit.

gubble

Amp has been fixed already !

Apparently the amp had a couple of bad solders on the IT rails (I've no idea what that means) and the power valves were indeed shot.

He's put a new set of Mesa Boogie 6L6's in there - would have been nice to been given the choice in valves but there you go.

All done and rbiased £115

jpfamps

gubble said:

Amp has been fixed already !

Apparently the amp had a couple of bad solders on the IT rails (I've no idea what that means) and the power valves were indeed shot.

He's put a new set of Mesa Boogie 6L6's in there - would have been nice to been given the choice in valves but there you go.

All done and rbiased £115

That may the LT rail......

DJH83004

Quite possibly the 470 ohm dropper resistors de-soldering themselves and destroyed the tracks in the bargain, I've got one in now with exactly the same issue. Ideally they should be replaced with longer lead ones and lifted well of the board to improve airflow or higher wattage if you can squeeze them in. regarding the Mesa valves, they source them from a number of different suppliers (and lets be honest there aren't that many!), the last set of Mesa 6L6s I examined looked like EH, and their pre-amp valves are very often badged JJs. Anyway glad it is all sorted