He must be a newbie. I've worked with toobes since the late 60's. Little teenie ones that have to be soldered in place to toobes as tall as myself costing 100k+ USD.
I just got my Audio Aroma FU-29 yesterday... the newer version fortunately. It had an interesting odor of what industrial China must smell like... most of that odor has since dissipated. I bought mine from Ebay seller "Tubestein" It was very well packaged and it arrived from China via UPS Express saver in just two days. In fact I was out of town assumming it would take a couple of weeks to get here and that I'd deal with it when I got back... Not the case though and not even so much as a dent in the box. The toobes were labeled as to which socket they are supposed to go into, I assmue because they biased it correctly. Got the thing hooked in and after an hours warm up all I can say is WOW! This thing blows most other 35 watt per channel toobe amps out of orbit including any of the beloved but more expensive Dynaco Stereo 70 modded amps. I've run it probably a total of about 10 hours by now and the toobes are still holding their own. When I ordered the amp I also ordered a quartet of GU-29's fomr Russia. Well... all four of those toobes are gassy and cause the amp to actually motorboat, I will see if the seller makes good and if he won't I'll leave him negative feedback. The getter on the inside of all four toobes is a bit cloudy indicating they are gassy. I also managed to score one NOS RCA JAN CRU-829B toobe and I have a couple more of those comming as I'm not expecting the FU-29's to last very long. I think one would have to spend several thousand to get an equivelent USA built amplifier that sounds near this good.
Mark
Mark
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The sockets on that amp look like those cheap ceramics that have the contact rivets almost flush with the top of the socket, right under the chassis. Do they use a mica or any kind of insulator between socket and chassis?
Been there done the Magnavox thing. Good but no where near as good as the FU-29, better than a Stereo 70 though. This amp is certainly no more dangerous than any other toobe amp is. One thing... give the amp a couple of minutes for the high voltage to drain off before removing the output tube plate caps. You could be in for a surprise there! The fuse in the FU-29 is correctly sized and it's built in an all steel chassis. Resistors may not be top notch but they are carbon film and judging from the posted pictures of other's burn't up resistors they are also flame proof. Now I certainly don't expect much life out of the Chinese 829 tubes but so far they have been fine and I'll run them till they fail at which time I'll put in a pair of JAN CRC-829B's made by RCA many moons ago. Best thing is that even brand new Cetron 829B's are under 30 USD. Probably will upgrade the power supply a bit and the two coupling caps. The toobe sockets are spaced slightly down under the chassis so no short circuits can happen. Am considering making the 829 toobe sockets one of my upgrades either to some old EF Johnson sockets or the new Chineese PTFE type sockets that also look really nice.
I don't think it's the valves you have to worry about : it's that little power supply circuit board with the relay on it where things go wrong.
well, my amp i doing it again...
this time the left gu29 red plated on the inside half of the tube. no bad smell or anything. it has run for a few 100 hour since it did it last time, but once again at low volume and for no apparent reason it has done it again,
there is obviously something wrong with it and i don't have the expertise to fix it i can look at a schematic and what out what is what but i don't like my chances of finding a fault unless there is a visably damaged component like last time.
has anyone else had the power tubes red plate and what was the cause?
thanks!
this time the left gu29 red plated on the inside half of the tube. no bad smell or anything. it has run for a few 100 hour since it did it last time, but once again at low volume and for no apparent reason it has done it again,
there is obviously something wrong with it and i don't have the expertise to fix it i can look at a schematic and what out what is what but i don't like my chances of finding a fault unless there is a visably damaged component like last time.
has anyone else had the power tubes red plate and what was the cause?
thanks!
Mine is probably approaching 50 hours of operation now. I lost one 6N1 tube but thats it and replaced them both with Russian tubes. I pulled the Chineese FU-29 tubes in leiu of a pair of RCA JAN 829B tubes that I got on Ebay. I let them burn in for a couple of days and then set the bias to .5 volts grid to ground as instructed. The result is a much smoother sounding amplifier and it has moved me 10 rows closer to the performance. All in all my FU-29 just keeps on ticking and sounding great.
If you keep having problems loosing tubes or with red plates get your self some real tubes.... like GE, RCA or Sylvania. Cetron still makes brand new 829B's. Be sure they are properly biased as it makes a huge difference on sound... Note: I ordered and got a matched quad of GU-29 tubes from Russia. All 4 of them are bad!!
Mark
If you keep having problems loosing tubes or with red plates get your self some real tubes.... like GE, RCA or Sylvania. Cetron still makes brand new 829B's. Be sure they are properly biased as it makes a huge difference on sound... Note: I ordered and got a matched quad of GU-29 tubes from Russia. All 4 of them are bad!!
Mark
i hope you did not trash those tubes....
a friend gave me two of these russians that did not work
when first inserted into the socket.
so what i did was to sand the pins with a 400 grit paper
and then with 1000 grit, cleaned with a toothbrush
and lo and behold, the tubes worked....
i chanced upon this method when i got a bunch of 6C33 with the same issues...
Piero7 .. Mybe you should do schrmatics in nice form (pdf ..) for all DIY newbies.
I do like 12AX7 ...but prefere 5751.
I will make video on you tube between those tubes.
I do like 12AX7 ...but prefere 5751.
I will make video on you tube between those tubes.
Hi, that amp can be problematic.....so what did i do with it?
1. i lowered the G2 voltage to just slightly lower than 200volts..
2. discarded the fixed biasing and used cathode biasing instead....
3. i used a cathode resistor of 250 ohms 5 watts bypassed with 220ufd/100 volt ecap..
4. replaced plate caps with ceramic types....
5. i added 2.2k carbon comp grid stoppers on the output tubes...
after that the amp amp behaved very well....the owner was happy....😉
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