chiguy

Well, I think I found what was wrong, bad soldering on the wire going from the pot to the PCB. I noticed that if I pressed on the pot I would get something louder in the left channel so I figured something was going on with the pot. I removed the wires to measure the resistance of the pot and in the process, noticed that the left channel wire had come off the PCB entirely even though my iron never went near the solder joint. I looked at the solder joint and all I saw was a round dome of solder with nothing sticking out of it. I've also replaced the electrolytic caps. As a result, I've noticed that the drifting while adjusting the bias/offset is not as rapid or large. Thanks for your help everyone!

Apparently when my friend bought this amp, it came with 2 sets of tubes. One of the first things he did when the left channel wasn't working was to try the other set of tubes. According to him, this would sometimes fix the left channel and sometimes not. I have new caps on the way. Is there anything else should I be looking at till then?

Just wondering if you are still running a group buy. I'm close to finalizing what I need.

Just curious, has anyone put together a BOM for the KGSSHV mini PSU? I've been looking at semiconductors so far. I've been looking at this BOM and am noticing different semiconductors compared to the latest version of the mini psu, https://docs.google.com/spreadsheet/ccc?key=0AnqARwsQ1QV7dG44Z2lZUnAwN3B0VE1Ub2xhLXN2U2c&hl=en_US#gid=0 What I have so far for semiconductors. I'm not sure if all of these are suitable however. 4x 2N3904 http://www.mouser.com/ProductDetail/Central-Semiconductor/2N3904/?qs=sGAEpiMZZMshyDBzk1%2fWiw99kSkYzPxmf7NzGOknJzA%3d 4x FQPF8N80C http://www.mouser.com/Search/ProductDetail.aspx?R=FQPF8N80Cvirtualkey51210000virtualkey512-FQPF8N80C 3x IXCP10M90S http://www.mouser.com/Search/ProductDetail.aspx?R=IXCP10M90Svirtualkey65120000virtualkey747-IXCP10M90S 6x 2sa1486 4x KSC5026M http://www.mouser.com/ProductDetail/Fairchild-Semiconductor/KSC5026MOS/?qs=%2fha2pyFadugoJzb5kdHGb1mz%252bVf84Up2OEtCwNu0mTI%3d 2x LT1021-10 http://www.digikey.com/product-detail/en/LT1021DCN8-10%23PBF/LT1021DCN8-10%23PBF-ND/891397 8x STTH512FB http://www.mouser.com/Search/ProductDetail.aspx?qs=8M15sSGRUn9rlB8mv3qAqw%3d%3d 1x 7815 http://www.mouser.com/Search/ProductDetail.aspx?qs=VOMQJJE%252bBNmeOJuT6KI25w%3d%3d 1x 7915 http://www.mouser.com/Search/ProductDetail.aspx?qs=%252b9%2fcbd0IE0T0iTVdYUTt3Q%3d%3d

Interesting, thanks! So I lost the left channel again. I took the tubes out last night to measure the lead spacing for the new caps. I put the tubes back to what they were before and the left channel was gone. I swapped the tube positions and the left channel was still gone. All four LEDs were lit in each case. I haven't gotten another set of tubes yet but that's the next thing I will try.

I'm putting in an order for these caps unless you guys have better suggestions. http://www.mouser.com/Search/ProductDetail.aspx?R=UKL1V470KPDANAvirtualkey64700000virtualkey647-UKL1V470KPDANA http://www.mouser.com/Search/ProductDetail.aspx?R=UBT1A221MPDvirtualkey64700000virtualkey647-UBT1A221MPD http://www.mouser.com/Search/ProductDetail.aspx?R=ECA-1HM100Bvirtualkey66720000virtualkey667-ECA-1HM100B http://www.mouser.com/Search/ProductDetail.aspx?R=EET-ED2G101CAvirtualkey66720000virtualkey667-EET-ED2G101CA Dumb question here. I'm curious as to what the glass components are in the attached picture. I know the ones on the ends are capacitors based on the silkscreen markings but I've never seen that type before.

One more thing, the bias voltage was around 420VDC using the ground tab on the back. I thought pro bias was 580VDC? I measured the normal bias using the ground tab at 185VDC.

I swapped the tubes back to their original positions but the Left channel is still working. I left the amp on for more than 6 hours before I started measuring the offset/balance. I was reminded of how extremely sensitive the trimpots were. Are there multiturn replacement pots that I can use instead? The right channel drifts rapidly. R+/R- started at -2.2VDC and drifts between -0.5VDC and -1.3VDC. I adjusted to drift between -0.3VDC and 0.6VDC. R-/Ground tab on the back drifts between 0.7VDC and 1.6VDC. R+/Ground tab drifts between 0.15VDC and 0.7VDC. I adjusted to drift between -0.1VDC and 0.55VDC. I re-measuerd R-/GND and it drifts between -0.3VDC and 0.95VDC. The left channel drifts rapidly. L+/L- drifts between -1.5VDC and 0.25VDC. I adjusted to drift between -0.5VDC and 0.7VDC. L-/Ground tab on the back drifts between -1.05VDC and -0.5VDC. L+/Ground tab drifts between -2.4VDC and -1.75VDC. I adjusted to drift between -0.4VDC and 0.55VDC. I re-measuerd R-/GND and it drifts between 0.65VDC and 1.5VDC. I will be putting in an order for caps soon. I've read that the large caps are the snap in type and everything else are standard through hole?

I should also add that the last time the left channel was acting up, it started working again after my friend cleaned the dust off the circuit board. It then stopped working again while listening to some music a couple of months later (which was last week).

I don't have a spare set of tubes at the moment but I will see if I can get some. Before going to bed last night, I swapped the tube positions (on a whim) which got the left channel working again. I'm going to swap them back later tonight and see if I can replicate the problem. I turned it on this morning to check the LED's and all 4 were lit. I'll measure and reset the offset/balance when I get home from work tonight.

A friend of mine has asked me to look at his vintage SRM-T1. The caps are all vintage so I will be replacing them. I count 10 electrolytic caps in there. 4x 400V 100uF 2x 10V 220uF 2x 35V 47uF 2x 50V 10uF The left channel has very weak sound. You can barely hear it when the volume knob is turned up all the way. The right channel is perfectly fine however. I'm not sure where to start troubleshooting this one. Unfortunately, I do not have another pair of electrostatic headphones to try. The left channel has worked before but it seems to work intermittently. I adjusted the offset and balance when he first purchased the amp a few months ago. Am I missing anything else that I should be doing with vintage Stax amps? Thanks!

Payment sent. Thanks for an awesome group buy!

I'm really tempted but the cost of parts for a T2 is big pill to swallow.

That list is what I have so far. I have the .1uF caps separated into 4x 450V and 5x 630V but all 630V caps will work also. Tube sockets, a pot, and terminal blocks are all that remain.

With the group buy of boards going on, I've been putting together a BOM for the Megatron. I will post a link once it's more complete. I have a few questions. What tolerance and wattage is recommended for the resistors? Are 680K Ohm or 690K Ohm resistors used? I'm looking at the jpg of the amp board and that number is hard to read for me. I think it's 680K after looking at Spritzer's populated board but I wanted to make sure. There is one capacitor (in the corner) labeled as .1uF / 4630V. I presume this is a .1uF / 630V cap? There are two caps labeled as .47 / 50V. Is this .47F or .47uF or something else? Thanks!

Are there issues with Dale?

I'm interested but I'm still deciding on what I need/want.

Will there be a Megatron PSU board also? The one found here:

+1 for megatron