| Author | Message | ||
| David V. |
Hi...Just sold a 212 HD-130 to a gal in L.A. Upon arrival, she blew out the amp fuse somehow, and took it to a repair shop (Gregs on Hollywood - Vine and Melrose). He went ahead and put NOS GCA7 power tubes in at $60.00 a pop (x4!). I called him to ask why, and he said that they were the only tubes that will take the high voltage plate current of these amps. I shipped the amp with what I thought to be the original EL34's, that I ran with no problems for the last half year that I owned the amp. I also had a EH 12ax7 (brand new) installed prior to shipment, which he pulled and put in a JJ's 12ax7. Anyway, I need to know if the data he supplied regarding the power tubes is correct? I personally think it's a crock, and at $60.00 a tube, the new owner took a bath? Any help? | ||
| Steve Kennedy |
He is somewhat correct but it isn't black & white. These amps were originally designed for 6CA7 output tubes, primarily because they can handle the high plate voltage. Most owner's use EL34 types because of the problem with obtaining affordable matched pairs & quads of the NOS 6CA7 tubes. The EL34 isn't quite as forgiving of high plate voltage as the original 6CA7 (due to the internal mechanical layout & element spacing). Some cheap or microphonic EL34 tubes may have enough movement of internal tube elements to arc-over when the amps is run in the high-power mode. Output tube plate voltage in the High Power mode exceeds 700Vdc, while it is typically closer to 400Vdc in the low power mode. It is possible that one of your output tubes was damaged or shocked in shipping or handling by the new owner and THIS was the cause of the failure. Output tube failure can also be caused by that 12AX7 phase splitter tube, so replacing that at the same time IS a prudent move. Why take the chance that an intermittant 12AX7 will take out $240.00 of NOS output tubes! The choice of the JJ is a good one, but I don't think that the brand is the issue here. I think the issue here is.... using a modern EL34 can be a crapshoot anyway. The tech probably would NOT guarantee his work unless the proper tube was used. I can't blame him there, but I think you should ask the owner if a "no-fault" EL34 replacement was even offered. Good quality EL34 tubes seem to work fine for many people, you just have to pay attention. Not all modern EL34 tubes are built to the quality of the Mullard and Amperex EL34 tubes you find in many Music Man amps. I ALWAYS recommend that people run their Music Man amplifiers in the Low Power setting unless absolutely necessary. This will dramatically extend the usable lifespan of modern EL34 tubes in this application. If you run them at High Power all the time, be prepared to replace them every 2-6 months depending on how hard they are electrically, thermally and mechanically abused. Using a small fan to keep the tubes cooler can also help, especially in an HD130 running balls-to-the-wall all the time at high power! Steve | ||
| Anonymous |
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| OZ of Atlantis |
Hello, I 'm needing some advice on re-tubing my Hd 130. Before I go into that, let me say thanks for a great resource and advice forum, and thanks to Steve for his broad knowledge. Now to my issue. Currently and upon purchase, my HD 130 came with Sovtek 8551wxt's. I thought nothing of this, as I'm ignorant to many of the subtleties and prejudices of different tubes, and they're uses. But now I'd like to re-tube, and so I got a matched Quad set of SED SV6L6GC tubes,before checking the pluses and minuses here. Question is, did I just waste my time? Will I need an amp bias, and are these tubes not up to the job, even though the Sovteks have been doing well, and TubeDepot recommends the SED'S as an upgrade, in terms of warmth, reproduction, and lowered microphonics of the tubes. So, now I've made my mountain out of a molehill, should I get a shovel? | ||
| mike kaus |
First off, you have to make sure WHAT tube your ampwas designed for. Have you looked at your tube chart inside the amp to see what tube it needs. I don't remember the 130 using 6L6's-they used 6ca7's or EL34's. The later amps were 100's and 150's so I'm doubtful that you have the right tubes. Even so, if you DO have the proper tubes, you should have the amp biased properly as the tubes today(and back then too) vary greatly on control voltage required to control electron flow in a tube. SED's are fine tubes, IF you can use them. Read your tube chart, than let us know, but if you do use 6L6's, thay are good tubes. | ||
| ogdave |
I had an amp tech install 6L6 by mistake in my 112 Sixty Five. They got so hot they were smoking. Thats what made me look at the tubes.I took it back and he put in the correct 6CA7.And it ran nice and cool again.I asked him if the 6L6s biased correctly and he said my amp had fixed bias. Is that true ? It is a 1974 model 112 sixty five. I don't think this guy new what he whas doing when it came to Music Man amps. He also put many small tears in the tolex and slight damage to the grill cloth to what was an amp I had babied for thirty plus years. This was in Nashville with a tech that has been around for many years.You never know who to trust with your baby. Now I am hesitant to take it in to some where else and have his work checked . Can any body recomend a good amp tech in Nashville that knows Music Man amps? | ||
| mike kaus |
Not familiar with Nashville but MM amps ARE not the same as Fender amps and these <techs> REALLY need to realise that. If your amp has a 12ax7 PI tube, have it biased(or do it yourself) to around 23mA of IDLE current and you'll be fine. |
Tue, 03/25/2014 - 09:26
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