CAV45s2 problems

[mb118]

Hi there,

Recently got a used CAV45-S2. Connected the amp to the speakers, installed the tubes and fired it up for biasing and the EL34 tube plates started glowing cherry red and blew the left channel F2 ceramic plate fuse. I turned the bias back down on each trim pot (counterclockwise all the way) and replaced the fuse. Started it back up and the bias lights turn on after a just a few seconds, tube plates get cherry red still. Correct me if I am wrong but I should not see the LED light up at full back counterclockwise, correct? Any ideas what is happening? I've tried 2 different sets of 5685 and 6922 but unfortunately don't have a replacement quad of EL34's at the moment. Seller tested the EL34's prior to packing them for shipment and this seems more like something wrong with the amp, but could be wrong. I have an email into CJ tech support but understand they are slow to respond at the moment.

Thanks,
Matt

[admin]

Normally the LED's would turn off by coutnerclockwise and turn on with clockwise rotation.

I think there may be something wrong here as tubes really shouldn't blow in a matter of seconds even if the bias is off. Also, by turning the bias controls counterclockwise fully they should be "under" biased and the LED should be off.

If you are brave enough to experiment, you can move the affected EL34 into another position and see if it happens there as well. If so, then it's a bad tube. If still happening in the original slot, then it's something with the unit and not the tube.

I would also let the seller know asap as it may be worth just sending it back or working out something that is reasonable for both parties.

[mb118]

Thank you. Will try switching tubes around when I get off work but it seems to be affecting multiple EL34s and report back. Seller is aware and is helpful and trying to assist as best as possible with the troubleshooting before we look at any other return/servicing options. I'd like to keep the amp if possible.

[admin]

Oh, I thought it was just one tube that was causing the issue. If it's affecting all the tubes, then most likely it's something with the unit itself and not the tubes. That would require opening her up and taking a look. Unfortunately, there are no schematics published for the SAV45s2 so you would be kind of on your own. But certainly you can look for any obvious signs of damage, burn marks, bulging caps, a bad solder joint, etc...

[AnotherJohnson]

RJ says bias current off is full clockwise with LEDs on. He shared this in another thread. He swore by it in spite of others, including myself, taking the view you’ve shared.

Regarding redplating, it could be some issue with the amp, but I would tend to think it is the tubes. Either they were marginal when they left the seller, or they were damaged in shipping. Another possibility is a short across the speakers. Are the wires 100% separated? Are the speakers known to be good (without an internal impedance anomaly)?

It could be something else. But the tubes and speakers are low hanging, albeit expensive, fruit.

After the tubes and speakers, you’ve really got to open it up and look. There are high, potentially lethal voltages inside, so don’t do this if you’re not qualified.

[AnotherJohnson]

FWIW, the CAV 45 S2 is new enough that it should not need to be recapped. Since the plate fuse blew, the bias resistors are probably ok.

Also … call CJ. Call daily until they answer. It’s a small shop. Email doesn’t always get the quickest check.

The more I think about this, the more I wonder about the speakers. Are they known to have played properly when hooked up to another amp?

Is your CAV volume turned down or is it muted? Is your source known to be compatible (normal streamer, CD, TT preamp?

[mb118]

I read this as well on the forum, but it doesn't jive with the manual. The manual says you may have to turn clockwise to get the LEDs to turn on. All the LEDS go on within a few seconds when the bias trim pots are turned max counterclockwise and the tube plates start glowing cherry.

This has occured with 2 different pair of speakers that worked fine with other amplifiers. I'm going to try and order a replacement quad of EL34's at some point soon as I agree, best to check the tubes first.

Thanks again for the reply, appreciate it!

Matt

RJ says bias current off is full clockwise with LEDs on. He shared this in another thread. He swore by it in spite of others, including myself, taking the view you’ve shared.

Regarding redplating, it could be some issue with the amp, but I would tend to think it is the tubes. Either they were marginal when they left the seller, or they were damaged in shipping. Another possibility is a short across the speakers. Are the wires 100% separated? Are the speakers known to be good (without an internal impedance anomaly)?

It could be something else. But the tubes and speakers are low hanging, albeit expensive, fruit.

After the tubes and speakers, you’ve really got to open it up and look. There are high, potentially lethal voltages inside, so don’t do this if you’re not qualified.

[admin]

If all the tubes have the same behavior, I'm really questioning whether it's a tube problem.

[AnotherJohnson]

Not meaning to cast aspersions on the seller, who I’m sure would not intentionally include marginal tubes, in the present tube market many klinkers are being passed off as good.

Normally I would agree that since all are bad, the problem is elsewhere. But today …

I would not waste money on new tubes to test without CJ’s advice. So hang in there on the phone call idea.

I hope they don’t say “send it in.” I’d return to he seller instead if it were possible.

[mb118]

All good points, thank you both. If I don't hear back soon from CJ I will try calling tomorrow.

Thank you,
Matt

[mb118]

I think we are out of the woods. I got home today and opened up the chassis again and rechecked the fuses. The F2 fuse on the PC board looked a little off, like it wasn’t seated 100% properly. I took it out, bent the clips inward and reinstalled the fuse. Put everything back and fired it up with the trim pots dialed back full counter-clockwise and it worked, no more cherry red plates! Was able to bias in properly from there (turning clockwise until the LED turned red for each of the trim pots, then turned it slightly back counterclockwise until they went back out) - and have it playing now with my Joseph Audio RM25’s. So fingers crossed this does the trick. Thanks both for your responses.

[admin]

That's great to hear. Possible the bad connection on the fuse made it function as a resistor and that cause problems down chain.

Keep an eye on it for awhile but hopefully this fixes the issue. If so, that was a cheap repair!

[AnotherJohnson]

Very strange. A fuse not seated is like a blown fuse, and a blown fuse would protect, not destroy.

Very good. No cost solution. So …

Great that it’s working. I hope it turns out to a good choice for your system.

[admin]

If a fuse was not seated correctly, but still had the connection. Wouldn't it act like a thinner wire, meaning that the resistance would be higher? Resistance being inversely proportional to the square of the thickness. Since we don't have the schematic, we really can't be sure how the system works so it may be causing an increased current in the tube. I don't really know of course, just guessing to try and explain what we know of the situation.

[AnotherJohnson]

No
Certainly it could be higher resistance, but nothing has higher resistance than a blown fuse.