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AVA Ultravalve schematic?

bill-g

bill-g

AK Subscriber
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I'm helping a friend whose AVA Ultravalve just went dead, tubes glowing, B+ is there, a bit high at 460V. No signal out. Sort of guessing that a lower voltage PS has failed. He can't find his manual. Anybody know if Van Alstine included schematics in there, and does anybody have a copy they could share?

Will contact Van Alstine too.
Thanks,
Bill
 
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Look for voltages to the input gain and inverter stages, it's possible a common source feeds these stages to both channels.
 
Have sent a query to AVA, we'll see what they say.

Cademan, power supply is a good suggestion, but been there, done that. Which is why I'd like a schematic. While it's based around a Dyna ST70, and I've seen a schematic for that posted here, Van Alstine has several lower voltage supplies in there using solid state rectifiers, that I am too lazy (so far) to reverse engineer. Was hoping for a road map for this trip.
 
No, never worked for AVA, but did meet Frank briefly when I worked at Northstar Sound back in early 80's in my first tech job. Went out there to get some parts for an AVA amp that we had on the bench as a favor for a commercial sound customer. Fun to meet the man himself. I've never owned one, but respected them. My friend, the owner of this amp has gone through a couple of generations of AVA gear, and always felt they treated him well.

Just checked the spreadsheet of my tube inventory that I did when I had way too much time on my hands many years ago. It says I have qty 3, 6GH8's <somewhere> ;-)
Guess I'll dig them out and try swapping in, until I get my hands on a friend's tester, and hopefully see a schematic.
 
A volt or ohm meter should tell you which part is at fault without too much of a hassle.

No voltage (regardless of voltage) after a certain part means that that part is bad. Very simple without a schematic for me but personally I don't own or have a schematic for you. Sorry!

If there is no sound, there cannot be any B+ or else there is an open resistor in the power supply somewhere. Should't be too hard to test without a schematic.

EDIT: Can you show us a pic of your projects power supply area? I or someone here could probably show you what to look for aside from someone else here who may have a schematic for ya.
 
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bill-g said:
No, never worked for AVA, but did meet Frank briefly when I worked at Northstar Sound back in early 80's in my first tech job.
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Sorry for the unclear post. I was asking WaynerN because for some reason I have thoughts he's mentioned work for/at AVA.
 
whoaru99 said:
Calling @WaynerN

Didn't you (or maybe do??) worked with AVA?
Click to expand...

Yes, I'm here and I did work for AVA as the mechanical designer. I have the original Ultravalve prototype and one of the first production units. I do not have a schematic for the amp, but I know someone that knows everything about it and could help you thru your problems. His phone number is 651- 330-9871.

One question I have is that I'm wondering if yours has the diode mods done to the 5AR4 rectifier tube? I'm sure Frank went to Mary or Dean's house today for Turkey, but he should be back at the shop tomorrow (Friday).

BTW, these amps are very reliable, but that doesn't mean that there can't be a failure. Faailure is very rare. I have some SS stuff that is nearing 25 years with no issues.
 
if this is somewhat based on an ST-70, I'll guess it has a multi-section high voltage supply? Do all of those nodes have some sort of reasonable voltage? Just wondering if you lost a resistor or something that feeds the section that provides plate supply to the driver.
 
Just looking back at my content and realized I left this hanging (4 years ago!) and never reported what was actually found to be wrong with the Ultravalve. I actually got out my old textbook and read up on push-pull tube amps. The section pointed out that the coupling cap from the plate of the split load phase inverter to the grid of the output tube is a frequent point of failure. Light bulb went on over my head. It explained excessive plate current burning the 15ohm cathode resistor. The caps were rated for 400 working V, and are stressed to right about that value. Replaced them with 450V units having same PCB footprint, along with output tubes and cathode resistor. Think I did some filter caps as well. It's been working fine ever since. Turned out to be fun and vindicated the time spent studying on tube electronics in the early 70's. We started with tubes and moved on to semiconductors later. I still have that textbook, Electronic Communication by Schrader.

In the process, I had a pleasant email exchange with Frank VanAlstine himself, who I believe pointed me to an assembly manual that showed the PCB layout of a later, similar model. Also found a manual/schematic for the Dynaco Stereo 70 which was helpful.
 
bill-g said:
Just looking back at my content and realized I left this hanging (4 years ago!) and never reported what was actually found to be wrong with the Ultravalve. I actually got out my old textbook and read up on push-pull tube amps. The section pointed out that the coupling cap from the plate of the split load phase inverter to the grid of the output tube is a frequent point of failure. Light bulb went on over my head. It explained excessive plate current burning the 15ohm cathode resistor. The caps were rated for 400 working V, and are stressed to right about that value. Replaced them with 450V units having same PCB footprint, along with output tubes and cathode resistor. Think I did some filter caps as well. It's been working fine ever since. Turned out to be fun and vindicated the time spent studying on tube electronics in the early 70's. We started with tubes and moved on to semiconductors later. I still have that textbook, Electronic Communication by Schrader.

In the process, I had a pleasant email exchange with Frank VanAlstine himself, who I believe pointed me to an assembly manual that showed the PCB layout of a later, similar model. Also found a manual/schematic for the Dynaco Stereo 70 which was helpful.
Click to expand...
what a great read

hows that ultravalve doin these days?
 
As far as I know it's working fine. The, owner, who I usually see weekly at a happy hour, hasn't said anything, but since his hearing has gone bad and has trouble managing the hearing aids, I don't think he runs it much. This is a bummer because he is/was a talented musician/arranger, and has a huge record collection. He used to have us in for occasional listening sessions. I'll have to press him to see if we can do that again.
 
bill-g said:
As far as I know it's working fine. The, owner, who I usually see weekly at a happy hour, hasn't said anything, but since his hearing has gone bad and has trouble managing the hearing aids, I don't think he runs it much. This is a bummer because he is/was a talented musician/arranger, and has a huge record collection. He used to have us in for occasional listening sessions. I'll have to press him to see if we can do that again.
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thats tough there. man i hope ur buddy finds a good way to manage that. happy listening, buddy.
 
That is good to know, do you remember what coupling caps it originally came with. My Ultravalve has rectangular dipped brownish red caps. I know Mr Alstine didn't believe in using fancy caps. I have seen pictures of an Ultravalve using larger caps in a molded rectangular blue capsules. I think they were Wima. My Ultravalve does have the diode rectifier mod. It is a wonderful sounding amplifier.
 
dipped brown-red sounds a bit like a Cornell "brown drop", their equivalent of a Sprague orange drop. The ones I'm familiar with are a mylar film cap, very reliable but nothing special.

Panasonic also makes a couple in that color family. ECQ is a metalized polyester (mylar) and ECW is metalized polypropylene. I've also used these with decent results. I had a single ECW go leaky but it possibly got over-heated.

The C-D caps are a lot more brown, the Panasonic are more reddish.
 
gadget73 said:
dipped brown-red sounds a bit like a Cornell "brown drop", their equivalent of a Sprague orange drop. The ones I'm familiar with are a mylar film cap, very reliable but nothing special.

Panasonic also makes a couple in that color family. ECQ is a metalized polyester (mylar) and ECW is metalized polypropylene. I've also used these with decent results. I had a single ECW go leaky but it possibly got over-heated.

The C-D caps are a lot more brown, the Panasonic are more reddish.
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I've used the Panisonic ECW's a lot. So far not a single problem with them.
I've used them for coupling caps in various preamp and amp builds.
I wasn't going to put together another amp, but I'm gathering bits for a 6L6 SE amp. I already have the OPT's, tubes, and a power trany on hand that will work. I'll most likely use ECW's since I have various values on hand.
 
Yeah I'd use them again with no fuss. I can't swear the failure didn't have some other explanation.
 
Hi, reviving this thread for a related question. Can someone share the position of the coupling caps on the PCB board? I’m looking for the R #; a description would be a plus. I would like to experiment with these. Also, if there is a thread on the rectifier diode mod I would be interested in learning more about it. Thanks, AJ.
 
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