Help fixing custom tube amp signal problem (sound only coming out of one side)
Hi there! I received a DIY stereo tube amplifier as a gift from a friend's dad a few years back, and I recently brought it out of storage and fired it up with some KG4 speakers. Unfortunately, it started smoking a bit and a tube started sparking a bit at the top. Tightened up two loose connections and the amp is working, but it's only emitting sound on one side. Any ideas on how to get started troubleshooting and fixing this? Thanks in advance.
Amp: Amp - Album on Imgur
Hi there! I received a DIY stereo tube amplifier as a gift from a friend's dad a few years back, and I recently brought it out of storage and fired it up with some KG4 speakers. Unfortunately, it started smoking a bit and a tube started sparking a bit at the top. Tightened up two loose connections and the amp is working, but it's only emitting sound on one side. Any ideas on how to get started troubleshooting and fixing this? Thanks in advance.
Amp: Amp - Album on Imgur
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Thanks. I have since dusted everything. I think I'll need to take this to a professional, but first I wanted to drop a note here to see if there's anything I could do before that as I'm curious to learn about DIY tube amplifiers and do have a bit of experience soldering guitar equipment. I know nothing about amps, but I'm willing to risk death if I can get that sweet Klipsch working on both sides.
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Thanks! It's great, the sound is amazing even through one speaker.
I don't have a voltmeter but could pick one up. I also don't have the schematics, but I'll see what I can figure out.
In the meantime, here's what I could gather about the tubes:
In the front row, there's a pair of Russian Г-807 (VIII 80) tubes from 1987 and a pair stamped 0 OTK, as well as a single tube in the center stamped RCA DR (maybe a 6? just a guess). The smaller tubes behind that front row are an OA2 & OB2.
Thanks for your help!
I don't have a voltmeter but could pick one up. I also don't have the schematics, but I'll see what I can figure out.
In the meantime, here's what I could gather about the tubes:
In the front row, there's a pair of Russian Г-807 (VIII 80) tubes from 1987 and a pair stamped 0 OTK, as well as a single tube in the center stamped RCA DR (maybe a 6? just a guess). The smaller tubes behind that front row are an OA2 & OB2.
Thanks for your help!
807 is a sweet Pentode output tubes. 0 OTK is not a tube number/name. It indicate a type of military surplus. My guess that the two other tubes likely are a dual triode of some type used as pre-amp. OA2 and OB2 are regulation tube indicating that it might have used regulated screen voltage, a good feature. The remaining (center) tube looks like a rectifier tube.
A good starting point is to isolate the output tube (807) that belong to the bad channel. You can do that by tracing back from the speaker wire to the output transformer secondary (the two blue color metal unit). From there trace the primary wires to which tube it hook up to. This will give you reference on where to measure the voltages later.
The other post is correct. While operating, the amp you have can go up to 300-500Vrms, a deadly voltage. Before powering it up, learn where you can and where you can not touch. Also remember capacitors can hold high voltage many hours after power has been turned off. Do check out the tread on high voltage on top of the forum if you not already have.
Great knowledge, much appreciated! Regarding the two connections: A 350V circuit had become detached at one end, and the top connection on one of the output tubes was loose, causing it to spark. Unfortunately the wire leading from the bad channel tucks into the assembly and out of sight so it's difficult to trace, but my guess is that the tube that sparked is the one that is now causing the audio issues.
I used to think that, too, but apparently it means the same as a "QC" stamp on American goods.
Spark on the anode cap (top connector) is bad. The reason it sparked was because the loose connection caused a lots of back EMF generation (much higher voltage that the designer intended). If that is the channel that no longer have output, chances are something broke in that signal path. There should be three components in that signal path, the output transformer primary winding, the 807 Tubes and the Cathode resistor//bypass cap. There is a good chance one of these broke. The tube you can check by swapping left and right channel or better yet put in a new one. The other two, you can start with an ohm meter.
An externally hosted image should be here but it was not working when we last tested it.
Hi all, just following up on this. I swapped the tubes and the speaker worked on the other side, so I'm guessing it's a faulty tube. The connector where it initially sparked is looking a bit burnt up. I'm wondering if I can fix it somehow or if I should purchase a new pair of 807 tubes, and if so, which ones? These vintage Russian ones sounded great but not sure where I might track them down.
It will take right clicking over your link & open in new tab for the readers to see your picture. Better to be uploading pics here by using the attachments management menu under advanced options when pressing the Go Advanced reply button I ended up picking up a pair of these bad boys by Farenti Brimar for the British Military:
807 tubes matched prs./quads CV124 Farenti Brimar contracted for Brit Military | eBay
Fingers crossed!
807 tubes matched prs./quads CV124 Farenti Brimar contracted for Brit Military | eBay
Fingers crossed!
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