Hey guys,
I need your help as I've encountered a problem with my 300b SE.
I built it roughly 2 years ago and have zero issues during the build and since. It's powered up everyday and operated beautifully.
I recently sold it and shipped it to Its new owner however its arrived not working. The rectifier tube warms up however the driver and power tubes remain cold.
We've checked all the obvious things like the source, volume, correct input etc etc and it appers something has gone south with the power to the tubes.
Now, the new owner has connected his 6 ohm speakers (he thought they were 8) to the 8 ohm output transformers, could this have damaged anything?
I've suggested purchasing a new rectifier tube but otherwise I guess it a case of going through the checkout procedure?
Can anyone suggest anything?
Cheers guys!
I need your help as I've encountered a problem with my 300b SE.
I built it roughly 2 years ago and have zero issues during the build and since. It's powered up everyday and operated beautifully.
I recently sold it and shipped it to Its new owner however its arrived not working. The rectifier tube warms up however the driver and power tubes remain cold.
We've checked all the obvious things like the source, volume, correct input etc etc and it appers something has gone south with the power to the tubes.
Now, the new owner has connected his 6 ohm speakers (he thought they were 8) to the 8 ohm output transformers, could this have damaged anything?
I've suggested purchasing a new rectifier tube but otherwise I guess it a case of going through the checkout procedure?
Can anyone suggest anything?
Cheers guys!
Good idea.
So far I've tried to test things out with my one multi-meter but there's too much I don't know and people have been coming and going all day so I haven't been able to dedicate my full attention to it. Testing what I believe to be R30, (please see the attached photo) the reading I get is 400.
An externally hosted image should be here but it was not working when we last tested it.
Also, to be clear on everything . . .
I put the tubes in from small to large into their designated spots. Then connected speaker cables and phono. Then power cord, then powered on. Power switch lit up as it should and rectifier warmed up showing a nice mellow orange and with my ear right down to the unit, I could hear a faint buzz. Tried switching from one input selection to the next going slowly and didn't get any sound. Tried again with volume up pretty high and still nothing. Stopped the record and tried at maximum volume while brushing the stylus with stylus brush and still nothing.
I then noticed that although the rectifier tube was toasty, the other 4 tubes were dead cold. I then shut it all down and spoke with Gavin.
After that I also tried a cd player and even another turntable but still nothing.
I put the tubes in from small to large into their designated spots. Then connected speaker cables and phono. Then power cord, then powered on. Power switch lit up as it should and rectifier warmed up showing a nice mellow orange and with my ear right down to the unit, I could hear a faint buzz. Tried switching from one input selection to the next going slowly and didn't get any sound. Tried again with volume up pretty high and still nothing. Stopped the record and tried at maximum volume while brushing the stylus with stylus brush and still nothing.
I then noticed that although the rectifier tube was toasty, the other 4 tubes were dead cold. I then shut it all down and spoke with Gavin.
After that I also tried a cd player and even another turntable but still nothing.
I don't know if you misspoke but the rectifier is the only one that heats up while all the others stay cold.
Sorry it's a bad pic -
This is the area you need to check; the 6.3 volt AC for the filaments connects to the circuit board immediately adjacent to the two 1N5401 diodes. My finger is placed on the connection pads to the board. I have my leads soldered directly to the board - most builders seem to use terminal blocks.
The 6.3 volt leads have probably become dislodged from the terminal blocks, or the screwed down connection to the termnal block may have become loose from thermal expansion / contraction. The blocks perform a clamping action on the wire, so it is important to make sure the wire is properly placed in the block, and is actually clamped in place when the screw is tightened.
Let us know whether or not this fixes your issue.
Win W5JAG
This is the area you need to check; the 6.3 volt AC for the filaments connects to the circuit board immediately adjacent to the two 1N5401 diodes. My finger is placed on the connection pads to the board. I have my leads soldered directly to the board - most builders seem to use terminal blocks.
The 6.3 volt leads have probably become dislodged from the terminal blocks, or the screwed down connection to the termnal block may have become loose from thermal expansion / contraction. The blocks perform a clamping action on the wire, so it is important to make sure the wire is properly placed in the block, and is actually clamped in place when the screw is tightened.
Let us know whether or not this fixes your issue.
Win W5JAG
Attachments
Here's my suggestion: Pull all tubes except the rectifier tube. Measure the heater voltages on the driver tubes and the 300B tubes. Also measure the B+ (should be accessible on the anode pin of the 300B).
If the B+ is within spec (or a tad high as it's not loaded by the tubes when the tubes don't heat up) but the heater voltage is missing, debug the heater circuit starting from the transformer.
Measure the output voltage from the transformer on the filament winding. Follow the schematic and work your way to the tube sockets on the heater circuit. You can take all these measurements with the rectifier tube out. That will limit the number of nodes with high voltage and make the circuit a little safer to work on.
Tom
If the B+ is within spec (or a tad high as it's not loaded by the tubes when the tubes don't heat up) but the heater voltage is missing, debug the heater circuit starting from the transformer.
Measure the output voltage from the transformer on the filament winding. Follow the schematic and work your way to the tube sockets on the heater circuit. You can take all these measurements with the rectifier tube out. That will limit the number of nodes with high voltage and make the circuit a little safer to work on.
Tom
From the day I got the amp, the large heat sink was wobbly and I was sure that it shook something loose in transit. I had no time so ended up taking it in to a repair man near me that said that whatever it was it wouldn't be a problem for him to fix.
Turned out that yes, the heat sink had shaken loose the filament regulator (D1). He replaced that and after 3 months of waiting (checking in with him every few weeks) he finally called to tell me it was ready. He had said he had done the check out according to the tubelab.com page I sent him and that I was set to go.
I get it home and hook up some cheap 8ohm speakers, cd player and finally plug it in and power it on. Pure magic. Definitely the best I had heard these little speakers sound. I shut everything down half way through 1 song and went to take care of errands.
Later a friend comes over and I put on the same cd but this time into newly run in Alpair 10p's. After about 4 songs I hear crackling and hear the music cutting in and out. I look over to see one tube glowing blue. I raced over and shut everything down.
An hour later I hooked everything back up again making sure that I had everything plugged into the right place and securely. Things seemed fine for about 10 seconds when the same thing started to happen so I just shut everything down again and contacted Gavin.
The only things that have been replaced are 1st the GZ34.
GZ34/5AR4-STR TAD PREMIUM SELECTED - TAD Rectifier Tubes SELECTED
and 2nd, the triode
5842 / WE 417A (aka CV2642 ) Triode USA - NOS Rare & Vintage
Then lastly the filament regulator.
I can't find specs on this replacement so I'm hoping that someone can confirm from the picture that this is the correct replacement. Or the tubes for that matter.
Turned out that yes, the heat sink had shaken loose the filament regulator (D1). He replaced that and after 3 months of waiting (checking in with him every few weeks) he finally called to tell me it was ready. He had said he had done the check out according to the tubelab.com page I sent him and that I was set to go.
I get it home and hook up some cheap 8ohm speakers, cd player and finally plug it in and power it on. Pure magic. Definitely the best I had heard these little speakers sound. I shut everything down half way through 1 song and went to take care of errands.
Later a friend comes over and I put on the same cd but this time into newly run in Alpair 10p's. After about 4 songs I hear crackling and hear the music cutting in and out. I look over to see one tube glowing blue. I raced over and shut everything down.
An hour later I hooked everything back up again making sure that I had everything plugged into the right place and securely. Things seemed fine for about 10 seconds when the same thing started to happen so I just shut everything down again and contacted Gavin.
The only things that have been replaced are 1st the GZ34.
GZ34/5AR4-STR TAD PREMIUM SELECTED - TAD Rectifier Tubes SELECTED
and 2nd, the triode
5842 / WE 417A (aka CV2642 ) Triode USA - NOS Rare & Vintage
Then lastly the filament regulator.
I can't find specs on this replacement so I'm hoping that someone can confirm from the picture that this is the correct replacement. Or the tubes for that matter.
An externally hosted image should be here but it was not working when we last tested it.
Well ...
Re: D1: D1 is the filament rectifier, it feeds the voltage regulator for the power tubes. I'm at the office, but that looks like the correct part - they're not hard to find.
I don't like the idea of a heat sink on a heat sink, that seems dicey to me, but if it works OK, I wouldn't try to fix it. If the voltage regulator overheats, however, it will shut down and the amp will malfunction - but I don't know that crackling would accompany that, as I've not experienced that type of malfunction.
Re: crackling: Often a symptom of a bad connection between tube pins and their repective socket contact. I would check the 5842's - pull them and then replace them, maybe rock them in their sockets a bit. This is probably your malfunction. Sockets can, and do, go bad, but I wouldn't worry about that now.
Re: blue glow: May, or may not be, bad. Blue glow on the inside of the glass is normal flourescence- don't worry about this.
Blue, pink, or some other color glow within the internal elements of the tube structure typically indicates gas, is bad, and might cause the problems you are experiencing.
Win W5JAG
edit: I'm not crazy about Chinese 5AR4's - I've fried every one I ever owned, without trying. That one in your link may be selected, or whatever, but I still wouldn't trust it any farther than I could throw it. That tube malfunctioning could cause the problems you are describing.
Those 5842's in the link are garden variety 5842's, and should be OK.
Re: D1: D1 is the filament rectifier, it feeds the voltage regulator for the power tubes. I'm at the office, but that looks like the correct part - they're not hard to find.
I don't like the idea of a heat sink on a heat sink, that seems dicey to me, but if it works OK, I wouldn't try to fix it. If the voltage regulator overheats, however, it will shut down and the amp will malfunction - but I don't know that crackling would accompany that, as I've not experienced that type of malfunction.
Re: crackling: Often a symptom of a bad connection between tube pins and their repective socket contact. I would check the 5842's - pull them and then replace them, maybe rock them in their sockets a bit. This is probably your malfunction. Sockets can, and do, go bad, but I wouldn't worry about that now.
Re: blue glow: May, or may not be, bad. Blue glow on the inside of the glass is normal flourescence- don't worry about this.
Blue, pink, or some other color glow within the internal elements of the tube structure typically indicates gas, is bad, and might cause the problems you are experiencing.
Win W5JAG
edit: I'm not crazy about Chinese 5AR4's - I've fried every one I ever owned, without trying. That one in your link may be selected, or whatever, but I still wouldn't trust it any farther than I could throw it. That tube malfunctioning could cause the problems you are describing.
Those 5842's in the link are garden variety 5842's, and should be OK.
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Thanks very much Win.
Good to hear about the filament regulator.
The repair man had originally wanted to replace the heat sink with a smaller one because the weight of it bouncing in transit from England to Germany is what broke it in the first place. I insisted that it remain the same though as it won't move much at all now that it's home, Gavin said it's necessary and George Anderson wrote on his site;
" . . . It has virtually no ventilation (there is a Lexan cover which is removed in this photo), and plays for hours without issue. This is probably the worst case that you would encounter, so this is the largest heat sink that you would ever need. I used it because it was free. If you have a heat sink similar to this, and the space to use it, by all means do so. The cooler these parts run, the longer they will last."
Semiconductors | Tubelab
About the blue glow. It was actually quite pretty but as it was only one and I only saw it once I heard the crackle, I assumed the worst. It was in fact inside the bulbous part of the glass. Very much like photos I've since seen online so apparently no concerns there. No blue glow on the right side along with crackle then silence in the associated speaker was bad news but at least tells me it's something going on there. According to Gavin the right side has always been slower to warm up and the repair man mentioned it too. Apparently that wasn't a problem to actual functionality for either of them but I mention it just in case it is a hint towards possible fixes.
Very happy at the thought that it might simply be the 5AR4's. Which ones have you found to work best for you?
I'm tempted to swap in a spare of the same make I have BUT while taking the board out I noticed melted wire insulation from the volume pot to to R1 that concerns me. It was at the twist in the wires (white / orange wire ((R1)) melted onto the still intact white wire ((R2)) ) so I'll get small small heat shrink for it before I solder it back on.
In the mean time, even though the contacts all looked clean, I did as you recommended and cleaned them.
Sorry for such a long post but I wanted to be sure to mention everything up to this point for clarity. Thanks very much for your help so far!
-Deniz
It won't hurt to swap your spare in, and it may solve your issues.
The vanilla Sovtek 5AR4 is fine, and and I would expect that the upscale versions of it would work fine also, although not necessarily any better for the extra expense.
Any U.S. made, British made, Western European made, or Japanese made, 5AR4 will be fine, regardless of brand, and would probably outlive you. Sylvania made some really robust 5AR4's that were marked as 5V4GA. They can be branded Sylvania, Phillips ECG, and even RCA.
Many tubes marked "made in england" or "made in germany" are communist counterfeits marked to avoid import bans, and should be avoided unless you are certain as to what you are looking at. These can even turn up in U.S. JAN boxes.
Win W5JAG
I've checked all of the connections and they seem fine.
All solder points seem solid and I've cleaned all sockets and pins as well as made sure sockets are tight. Swapped out all of the glass as I had extras and problem still there.
Tube on left gets hot while tube on right only gets a faint glow. Left speaker has a soft crackle that doesn't change when turning the volume up or down. When playing music only the right speaker plays.
Since I don't have any spare 300b I let everything cool down for an hour then swapped those and same thing. No music from the left speaker, only a light crackle.
All solder points seem solid and I've cleaned all sockets and pins as well as made sure sockets are tight. Swapped out all of the glass as I had extras and problem still there.
Tube on left gets hot while tube on right only gets a faint glow. Left speaker has a soft crackle that doesn't change when turning the volume up or down. When playing music only the right speaker plays.
Since I don't have any spare 300b I let everything cool down for an hour then swapped those and same thing. No music from the left speaker, only a light crackle.
Not entirely sure what this means.
By hot, do you mean the left tube has an orange or red glow coming from the outermost metallic part of the tube ( i.e. the anode or plate ) ? This is bad.
By faint glow, do you mean the right tube is only emitting light from the innermost filament like structure ( also known as the cathode ) ? This is normal.
Do you know how to measure and adjust, if necessary, the power tube bias?
Win W5JAG
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