Sounds like a bad filter capacitor to me. |
Yes, a good suggestion, Ralph.
Along that train of thought, you can also start the amp up without the rectifier tube plugged in. That lets you see where the bias is without (hopefully) the amp going down, and get it right if it's way out of whack, or at least turn it way down. I would actually do this before firing up the amp with the rectifier in and the output tubes out.
Of course, this presumes the amp is fixed bias, and though we've not been told this (if I didn't miss it), have kind of been working under that presumption. A cathode bias circuit would open something else for him to think about.
There's a way to post photos here, Heyraz, but I've long since forgotten how. It used to be semi-common here back in the day. If no one comes to the rescue with that, I'll send something offline. |
Atmasphere: The first time the rec. went, it happened after 30 mins of use. The second time, it happened two seconds after power up. The amp is going back, but thanks for getting this back on track Atma. |
Devilboy, try starting up the amp with no output tubes in the sockets. If the rectifier blows, your filter caps are shot. Its a hellava way to find bad caps IMO, but you would know for sure.
The fact that it did this before and after power tube replacement points to the filter caps, assuming that the power tubes were biased OK. Is it also true that the rectifier would blow in fairly short order (seconds rather than minutes)? |
I think we pissed Devilboy off, but I'd love to see a picture of your tree. Even my wife would appreciate it. Merry Christmas!! |
You could use one of those 845s for the star at the top of the tree, Goldeneraguy! That thermionic beast would make one heck of a statement.
Though I've got a really cool true 5 bulb star from the 1950s or 1960s on my tree, this seems like a novel and fun idea. I have some 845s and 211s around, and might want to give it a try if the heat isn't too much to disqualify it.
Heyraz, the tubes I use have metal or polymeric bases, and as you would well know, there's a "pinch" in the glass where the base and glass couple together. From there, I use a sort of string/thread to tie around them on one end, with the rest of that material forming a loop to hang from one of the branches. It's simple/crude, but it what a lot of Christmas tree ornaments use, and it's worked well enough for me for probably 10 years now. |
That's my kind a guy "Class A all the way"! Do they hang from sockets or did you glue little hooks to the glass? You better get a patent before Hallmark finds out. |
Hi Trelja, Great idea.I have some EL 34 AND 845'S.That should light up the tree.
Happy Holiday
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Heyraz, yes, I absolutely decorate my Christmas tree with vacuum tubes. My wife thinks it's ridiculous, but I think it looks very cool. I used to know how to post a picture here, but have forgotten.
I did the same thing back then when I replaced the incandescent light bulbs in my house with CFLs. I was in a really cool store that was selling incandescent bulbs that were painted in things like snowflake motifs and stuff like that, and I stole the idea from them. I figured vacuum tubes would also serve the bill.
None of the tubes (or lightbulbs) are connected, electrically. They just serve as ornaments. I probably will one day when I have enough on the tree to make a meaningful statement. It would be just the heater filaments, so they light up. But, if they were biased, you can bet it would be Class A all the way.
Oh, one other thing to look at Devilboy is to make sure resistance in the bleeder circuit of the power supply circuit is high enough. If it's not, too much power will be present, and you'll be arcing over rectifiers with no trouble at all.
Speaking from personal experience and expanding upon what Ralph intimated, the Chinese are great at screwing up both the design and implementation of high-end audio products. I'm not sure how old your amplifier is, or how long you've used it without encountering this issue, but what I'm saying is don't assume they specified/figured out the right value of the resistor here or even if they did, that the right value was installed in your amp. Their piece to piece variability can often be breathtaking, sometimes making their own schematics look like downright works of fiction.
Continued luck in solving this problem! |
Could we get back to the issue here? |
Trelja-
You really decorate your tree with old tubes? I have some old dusty, busted up EL34s from a ST70 that I'm working on. The glass is mostly intact but separated from the bases. They each say Dynaco by Mullard. An authentic set of collectible Christmas Ornaments.
Just wondering-do they just hang or do you light them up too? If so, how are they biased??? |
A rectifier arcing over makes it ready for the dustbin. It's heartbreaking, not too mention a pain in the pocket.
Have you already disposed of your 274Bs? If not, and you're willing, I would be more than appreciative if you could send them to me. I decorate my Christmas tree with tubes(seriously), and the 274B would really look great! Of course, I'd be willing to cover all the costs in getting them to me, plus a bit more. |
Yes, I'm using slow blow fuses.
The rectifiers and fuses went before AND after I changed output tubes. The second time, electricity arched from one side of the rectifier to the other. Yes, I was told to check the filter caps and look into a short or bad solder joint. Thank you all for your input. I will post my findings ASAP. |
Detredwings gives the best advice, "Power supplies can be dangerous and if you don't know what your doing I would suggest you take it to someone who does. I'm only suggesting this because the high voltage stuff can hurt you."
As upset as you are, consider it a blessing that the rectifier and fuse are blowing before something more serious occurs.
If the filter caps do check out OK, look around for a heavy duty short somewhere in the power supply. After that, I'd be suspicious of the power transformer. |
I would not be surprised to find a bad filter capacitor in the power supply of this amp.
However, you did offer a clue to an alternative explanation:
You just installed a new set of 6550s in the amp. Did the rectifier by any change begin blowing after that? Are the 6550s properly biased? If not, this could pose a problem for the rectifier, *if* the power supply or the power supply design is somehow marginal.
IME the Chinese stuff is cheaper but you pay for it in service headaches. |
How do you know the rectifier tubes are blowing and not just the fuse? Are you using slow blow fuses? |
The previous response is correct. You have an over current condition. Since you keep putting tubes in it, my guess is you don't have any experience with this kind of thing? Power supplies can be dangerous and if you don't know what your doing I would suggest you take it to someone who does. I'm only suggesting this because the high voltage stuff can hurt you.
P.S. don't waste any more tubes until the problem is fixed. |
My first guess would be a bad cap in the filter section of the power supply. You seem to have an over current condition. Second guess would be a bad driver tube then maybe an output tube. I would have it checked out by a good tech. There are many more components than what I mentioned that could be the culprit. May even be a cold solder joint. All guesses. |
