Help ~ blown tube? HRD

[4real]

Hey guys, need some help here.

I have a Fender Hot Rod Deluxe that's worked perfectly for a few years, good condition, no rough use nor excessively loud.

So, in the last week I will occasionally get a low deep 'hum' and some loss of power. Looking in the back, I see one of the bigger power tubes GT6L6B is not glowing. Moving it slightly was letting it start to glow but would often die. Glowing tube, low noise gone.

So...is this the symptom of a dying tube.

Thought I would remove said tube to see if there was any obvious deterioration of mis colour or perhaps in the connections. No, looks like new...however, now does not glow at all it seems. So, Is Dead?

...

Right, assuming that it is a dead tube (I'd like some confirmation before going for a new one or pair), I have played this amp a fair bit so quite possibly it has gone, any suggestions or proviso's.

I'd also really like to fix this thing 'quick' and not sure of suppliers in Oz for such things so any suggestions there or valve choice and all that. Perhaps biasing, etc.

Ok, well thought I'd run it by you guys as I know very little about amps, particularly valve amps (it never happened to my old transistor things LOL.) Fortunately I do have a spare amp, but got a gig in a month and really would like this amp back on board.

[4real]

A quick 'update' on some good advice, I swapped the tubes over...the problem followed the tube so that would seem to indicate that it is a blown tube.

I've found a few suppliers and would seem a matched pair is the obvious thing to do. There is a lot of mojo speak about though.

I've found some EH6L6 tubes on special for instance ($62 the pair, + $12 courier)...are there valid reasons to select some brands over others, or suppliers.

While at it, would replacing other valves make much difference in this all GT fender...say replacing the preamp tube for EH while I am at it?

[yakkmeister]

Some things to consider:

Valves are made with considerably loose tolerance these days.

The Hotrod Deluxe is a push-pull amp.
Always change push-pull valves in sets - the valves are matched to work as efficiently as possible and failing to do this will result in ugly sounds and probably more blown valves.

I read that the Hotrod Deluxe is a fixed bias amp.
This means that the bias will need to be set using a CRO by an experienced tech. It may have to have resistors changed on the output valve's cathode or it may have a trim pot to do the job. Either way, it's an in the shop job; voltages in there are lethal and it's a job for a pro.
Having said that, if you are running "groove tubes" branded 6L6's you can order a set of those that have the same 'rating' on them. This will mean that the new tubes are within appreciable tolerance to the old ones and no biasing need be performed. If they are not groove tubes and you can get the original's tested (or know the specs) places like evatco can and will supply you with a set that will work with your current bias.

You get what you pay for. But valves on special are a good idea.

RS Electronics sells cheap, Chinese valves. These can be very good.
Evatco sells several brands and types - Russian valves may be had from here. Very generally, these tend to be more robust.

Hope that helps!

[andy]

I will second getting the bias changed by a pro. Swapping a valve is easy, but getting the thing running right is a specialist job, and while re-wiring guitars can get you the occasional burnt finger and swearing fit, a wrong move in the back of a valve amp can put you in a box in one fell swoop.

would replacing other valves make much difference in this all GT fender...say replacing the preamp tube for EH while I am at it?

I have experimented a little with different brands in various amps, and I'm afraid to say that in my experience, yes, different makes (or individual units) of the same type can and do sound different from each other. I've not been so scientific about it to say to what degree they sound different; some have been a night and day difference, others just a subtle shift, but both the EQ balance and drive characteristics can change just by swapping them for another unit/make.

In a fixed bias amp it is not really worth messing with the output valves unless you can bias them right each time, but a pre-amp valve can be chopped and changed without much hassle, and might be a nice way to fine tune the sound a bit. As with anything you may find you prefer one element of one, and one of another, and never really be 100% satisfied. If you're anything like me it's another slippery (and expensive) slope to get caught up on trying to get things 'just so'!

Anyway, if you'd rather side-step some or all of that, a good tech should have a supply of good valves in stock, so when you take it in to him to be fixed he should be able to get everything working at its best without too much input from yourself. If you were interested in experimenting with pre-amp valves he/she may let you try a couple of different ones which might be lying around, although in my experience, amp techs tend to think a little more 'technically' about the workings of an amp. To them a good working valve is a good working valve- it is us musos who notice/care to hear/IMAGINE that there is any real difference at all.

[4real]

Well, thanks for the replies.

I found this on re-biasing the HRD and this site offers similar video advice on other amps.

www.eurotubes.com/eurotubes-Hotrod-Deluxe-How-To-Bias-Video-6L6-6V6-millivolts-mA.htm

By swapping the good and bad valves that seemed to show it was a valve/tube and not the amp, which as I expected.

The EH tubes were on special so went with them and should only take a few days. Needless to say, living on an island...there ain't no amp techs, hardly any musicians...in fact being winter, not many people about either!

I did get some good advice from 'retro tubes' so would recommend them to any people down here and while it took a bit to get back to me and a little more expensive, kind of regret not taking that option.

Anyway, I am sure that the EH is at least as good as the GTs that came with the amp and to be fair have lasted years now without failure.

I got a matched set coming so that should be ok. The biasing seems not that hard and confusing in many respects, I thought it would amount to calibrating each valve but the amp does not really have that capacity without physically changing resistors and the like. As that video shows, it has a test point and a trim pot inside...and yes, lethal votages, which is why I tend against people building or doing much modding to valve amps.

In fact, for decades I used a transistor amp, it is still here, a few scratchy pots, but otherwise working as well as ever and quieter. It does not have that fender sound (it has that super clean roland sound!).

I guess, unlike a lot of players, I am after a little warmth, but basically pretty super clean. I do like the valve sound I admit, but unlike a player that relies on distortion tones and amp breakup and all that, well it's not a priority.

Anyway, we will see how it goes, yet another unexpected but inevitable expense but such is the way of things some times.

Reading all these reviews and opinions the Svetlana 6L6GC that retro amps could supply are most commonly praised for the amp, the EH is not a bad option and excel in the preamp stage. To test this out and because on special too and paying post, I thought I'd get one and see if there is much difference. EH's are russian I believe and are a decent quality and likely some improvement...though, I've been generally happy with it for what I do. Altronics is the supplier.

Thanks for the replies though, had a feeling it could be a lot worse!

[4real]

Would you beleive...they delivered to me=y door, in a storm, the very next day...a pair of matched EH power tubes and a pre-amp tube to try out within 24 hours. Amazing. Anyway, the amp works and seems 'brighter' and glow a little less 'red/orange' than the others were.

Do they need some kind of 'burn in' or something. I'll leave the bias for the minute as it seems to be fine, I like it 'clean' and it is set 'cold' apparently, but perhaps a little warmer when I get the nerve, it does not seem to hard to raise the voltage a little!

[4real]

So....

Tubes were replaced...and yet NOW...

A really annoying bass frequency constant hum is there. This was a very quiet amp and certainly not this noise. It's not a lud sound, inf act constant regardless of the volume of the amp or whether a guitar is plugged into it...hmmm...or should I say...Hummm...

So...not knowing much about such things, anyone hazard a guess as to the potential reasons and or solutions? I did not 'bias' the amp as described above, I did replace the pre-amp tube while I was at it, so have a 'spare'.

It might have been a problem that gradually started before the tube went, hard to say.

It is a low frequency and constant um, but weirdly, having that in the background does seem to give one a weird 'seasick' kind of feeling after a while.

Fortunately I have a spare roland SS amp that never had such hassles as tube amps do...for well over 30 years! A few scratchy pots perhaps.

[yakkmeister]

Not sure, mate.
I suspect that if you replaced the power tubes and did not bias it, then the hum may be due to there being an incorrect bias.

The hum may also be heater noise or something has failed/broken inside, a decoupling cap for example, causing noise.

[sumgai]

Pete,

Your tube orginally 'failed' due to a dodgy power supply filter cap. The new tubes will do the same, sooner or later.

If you're not comfortable messing around in there, a visit to your nearest trustworthy repair shop is in order.

Oh, and the bias supply likely has nothing to do with this. Not absolutely impossible, but very highly improbable.

HTH



sumgai

[4real]

Thanks Sum

I'll retire it for the while as I have a solid state spare, what a bugger. Unfortunately nothing local, but will arrange a trip as the valve thing did reveal a few...well....in the state!

It is something that people might consider with amps that there are good SS around and while tubes can sound gorgeous, they are fragile and not for 'tinkering' really...

Back to the Roland (which I returned to service yesterday and has some great clean if clinical sounds!)

[yakkmeister]

It is something that people might consider with amps that there are good SS around and while tubes can sound gorgeous, they are fragile and not for 'tinkering' really...

I disagree - Valve amps are totally for tinkering!
I rebuilt my valve amp about 3 times now... still haven't died.

It's actually not that difficult to replace the filter cap - just needs careful attention to voltages. A DMM, a resistor/path-to-earth and some care will put paid to the dangerous voltages. Then it's just a matter of replacing the caps. Sure, you need to know what caps to replace, what values to replace with ...
Plenty of good online resources to help you out there.

Don't go into it blind and don't be a cowboy - take care and you'll be fine.

Warning: It is addictive.

[4real]

Thanks...

Well, I would not rule out tinkering, largely inexperience with it than anything, am aware of the voltages in there. There are a couple of modes I would consider, mainly the stupid linear pot they have in the volume that means almost off the gain is between 1-2 on a dial that goes to 12!

It is a beautiful sound, certainly does those fender cleans well and has provided good service for quite a few years.

They are 'fragile' though and when you absolutely, positively, want something to work...SS definitely has it's advantages. I'm glad I still have the thing around that can do the job.

[morbe]

I had a Fender HRD ones, ONCE! ;D
dont get me wrong the amp sounds great! But for me the issues far outweighs the tone. my was first generation. I got it second hand of course and within the first week it would cut off at loud volumes. tube change did nothing! amp tech resoldered every joint on the board and finally fixed it. a year later it started blowing fuses, again tube replacements did nothing. took it back to the shop, the power transformer was dead. replaced the power transformer and it blew again! after mucho hours spent on the amp the tech I took it to called it. it was with a heavy heart my tech told me it would have to be rebuilt. And it would cost more.than the amp is worth in order to rebuild it. I hope this is not the case with your amp. but preamp tubes can make some pres amp tubes can make strange noise as well.

[4real]

Thanks, I Think!

Sounds like the problem the others described above symptomatically. I am aware that this amp has a reputation like that, yet it is one of the most popular amps and by sheer numbers and the way things are produced these days problem things will undoubtedly occur. This is the first time I've had a problem, it was secondhand but as new used in a home studio so had quite a few years of use before this.

I can't afford nor find a guy to service it just at the moment, and with this gig starting next week, can't afford to muck about with it just now. I've switched to the trusty SS roland which has run without problems for over 30 years LOL. It works, it's clean...but not like a 'fender clean' I will admit, very clinical, but will just have to lump it for now.

When I changed the power amp valves, I did change the 1st preamp valve, so I could swap it back, but I tested it before changing that one and I think the problem probably pre-existed all that, as they say above, likely the cause of the tube blow. Rather than risk having the problem spread further down the power stage, I'll rest it for now!