My HRD is sizzling but not in a good way.

It sounds like a cross between static, noise, and frying bacon. It's happening on both the Clean and Drive channels and to top things off it's intermittent. About six weeks ago I was having some other issues (viewtopic.php?f=13&t=74837), took the amp in for servicing where one of the pre amp tubes was replaced with a GT 12AX7-R3. The amp worked fine after that. Now the sizzling. I don't know if the two issues are related or if there's anything I can diagnose on my own.

Thanks & Cheers!
BM

_________________
This is the Blues. Are you listening?

.... more than likely a preamp tube. Use one known good 12AX7 tube to try in each position one at a time. Put the new tube in V1, no noise, problem solved. Still have noise, replace original in V1 and try the new tube in next position V2, up to and including V3.

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.

Hi shimmilou and thanks for the quick reply.

I'd be willing to try swapping tubes but it would have to be when the noise is present. Right now the noise is gone and everything is hunky-dory-dandy. Don't you just love intermittent problems.

Although I'm still a noob when it comes to the inside of tube amps, not to mention the fact that Bluesky636 and Arjay have put the fear of God Almighty into me about the dangers that lurk inside (I thank them for doing so!) - swapping pre amp tubes is something I think I could do in relative safety. While I'm at it I may as well change the sound to something a little warmer and more Bluesy. In a current thread you suggested replacing the stock 12AX7 tubes with 5751 tubes. However the OP of this thread was looking to tame the drive channel so I don't know if you would make the same recommendation in my case. (see Replacing tubes in Hot Rod Deluxe viewtopic.php?f=13&t=76024)

_________________
This is the Blues. Are you listening?

You don't even have to remove the back panel to exchange tubes. Just make sure that the amp is off, unplugged from electricity and tubes are cool. Yes, a 5751 in V1 and a 12AT7 in V3. If you want to tame mostly just the drive channel, a 5751 in position V2 would have the most impact. I would try swapping the tubes as suggested above and then see if the problem reoccurs, and not wait for the noise to appear first. Sounds like you might do well with a 5751 in both V1 and V2, and a 12AT7 in V3, and be sure to get good quality tubes. I have the feeling that the tube that your shop replaced before might very well be the one that is noisy, but it could be any of the three. As always, none of this is sure, just very likely.

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.

Thanks for the tube recommendation, shimmilou. I'll give it a go. As for good quality tubes, what would you recommend?

Ideally I would like to take the amp back to the shop and set things up so that I'm present when the technician is working on it. If this is not possible, then I'll go the DIY route. No worries, I'll make sure everything in the house is unplugged

_________________
This is the Blues. Are you listening?

For V1 and V2:
http://store.yahoo.com/thetubestore/jange5751.html
or
http://store.yahoo.com/thetubestore/sylvania5751.html

I like Sovtek, but I've had some of their 5751 add some hum in the V1 position in larger combos and some work well, but they will be fine for V2 if you want to save a few bucks.
http://store.yahoo.com/thetubestore/sovtek5751.html No need for 'Balanced" tubes in V1 or V2.

For V3:
http://store.yahoo.com/thetubestore/12at7.html Choose the "Balanced" option.

There are cheaper alternatives that might work well, I just listed what I feel are some of the best in this case.

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.

Thanks for the recommendations and the links. Great site with lots of info on amp tubes. I'm not sure I understand what you mean by selecting the "Balanced" option. The only option under "Additional Options" is "Matched Sections (+5.00)" which I assume applies to pairs of tubes. The only pair in the pre amp section would be the 5751s in V1 and V2 which, as you clearly state, don't need to be balanced so what is it I'm missing?

Regarding the choice of tubes, the tubestore site has a table of possible replacements for the 12AX7 and the corresponding gain level.

• 12AX7 | 100 gain
• 5751.. | 70 gain
• 12AT7 | 60 gain
• 12AY7 | 45 gain

Any opinion on the 12AT7 or 12AY7?

_________________
This is the Blues. Are you listening?

"Matched Sections;"

This means that the two triode sections within one duo-triode tube (like the 12A(_)7 series) are "matched" to each other. Mathced sections maybe important in phase inverter, but not in input and gain stages (V1 and V2). As these sections usually use each section for different purposes. And have them set to different electrical parameters.

The 12AY7 is a great tube. NOS ones can be a little costly. Esp the mil spec 6072. Ppl seems to like the Electro-Harmonix 12AY7. I never tried it.

You prolly won't hear too much gain difference between a 5751 and a 12AT7. Tonal differences are another story. A good 5751 is noted for its tone and long life. But, there are good 12AT7 out there, too. A sleeper is the triple mica Sylvania 12AT7WA. Tone is amp and ear dependent. So you'll need to do a little tube rolling, to find your niche.

Good luck!

http://tctubes.com/Sylvania-12AT7WA-triple-mica.aspx

BTW... you may want to try a little contact cleaner on the pins and sockets. this may help the periodic sizzle issue.

Yeah, thetubestore likes to have a lot of misnomers on their site, but they sell great tubes and have great customer service and guarantee. Matched always refers to output tubes, and balanced always refers to dual-triode preamp tubes. You can't match the two halves of a dual-triode, as they are both inside the same tube, you can only select ones that are already balanced, meaning selecting the tubes that have both halves with the same gain/balance between the halves. You can however match two different output tubes, or two different preamp tubes, to each other.

I only use the 12AT7 for PI myself.

As BMW2002Ti explained, for the PI tube you usually want a balanced tube, or as thetubestore misstates on their site "matched". I notice they also just started using the bullshit "JJ/Tesla" nonsense. I guess that they need to do something to make JJ sound more boutique or something to compete with better tubes. I think I'll start selling some Shuguang/RCA tubes, being as how Shuguang acquired some old RCA equipment and make a black Plate tube just like RCA did. Chinese RCAs.....

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.

Thanks for the clarification, BMW2002Ti. Whenever buying gear I try to do it locally so I called a few music shops but it turns out that they know even less about tubes than I do. "We don't have any 5751 tubes but we do have the Groove Tube 12AX7 which is 100% compatible." LOL!

I was ready to pull on the trigger on a pair of GE-5751s or SY-5751s but both are out of stock at The Tube Store. I don't mind waiting a few days to see if they get restocked but in case they don't, any other on-line suppliers you would recommend?

Thanks!
BM

_________________
This is the Blues. Are you listening?

http://www.tubedepot.com/nos-5751jan.html

A few dollars more than thetubestore, but they get the "balanced" option right, as well as offering "matched", which would be two separate tubes matched to each other (when ordering two or more tubes). Matching the two preamp tubes isn't really necessary unless you want to have a spare that is exactly the same gain.

They also offer an RCA 12AT7, but no option for balanced.
http://www.tubedepot.com/nos-12at7-rca.html

Or, a Mullard, with balanced available.
http://tubedepot.com/nos-12at7-mullard.html

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.

Thanks again, shimmilou. Just placed an order with tubedepot for a balanced Mullard 12AT7 and a pair of JAN-5751s.

Before swapping tubes I'll make sure that the amp is turned off, unplugged,
and that my rubber gloves, rubber shoes, and rubber suit fit nice and snuggly.

_________________
This is the Blues. Are you listening?

Funny, but you have the right idea, be safe when dealing with electrical devices.

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.

It's been ten days and the sizzling-frying bacon-static-noise I mentioned in my original post has mysteriously disappeared and not returned. In spite of this I went ahead with the tube swap and after a couple of hours playing time, here are my initial impressions.

Change is not dramatic: Maybe it was the excitment of changing tubes for the first time that had me anticipating a huge difference in sound but in reality the changes were more subtle.

Clean Channel: The amp is quieter. Prior to the tube swap I had the volume at 2 and couldn't go beyond 3.5 before hearing from my wife. Now I'm at 4 and there are no complaints until I get to 10.

I was expecting an early breakup on the clean channel but even with the volume dimed at 12 it still sounds pretty clean. Of course before I couldn't even get anywhere near 12 so there is no basis for comparison.

Drive Channel: This is where it seems we have the greatest change. Besides being more quiet (tamer), the timbre has changed from what I would describe as harsh (some say shrill) to a sultry, raspy, more Bluesy OD. I also believe there may be more tonal possibilities with the new tubes but this is yet to be determined.

Thanks to Shimmilou and BMW2002Ti for your input and recommendations. As alway, very much appreciated.

Cheers!
BM

_________________
This is the Blues. Are you listening?