Matching power tubes for an SVT-CL

[rickaddict]

Hi guys!

I have a (hopefully) quick question for y'all:

I just had my SVT-CL re-tubed by my local shop, and when I brought it back home and powered it up I noticed that the biasing LED's on the back of the amp would not light green. According to the manual, this means that I had a non-matched set of tubes.

So I called the shop back and told them this. The amp tech told me that those LED's and their circuit go bad frequently and that he gave me a "matching quad" of power tubes (The amp needs six matching tubes, btw). He told me to bring the amp back and he would re-bias it and disconnect the LED's if I would like, or for another $200 or so he could "fix" the circuit for the LED's. This didn't sound right to me, so I got online and ordered a matching set of 6 tubes to see if there really was any problem with my LED's. I got them yesterday and put them in, and sure enough the amp had no problem biasing and my LED's are now green.

When I removed the new tubes that my local shop had just put in, I put them back in the tube boxes that the shop gave me (which they presumably came in). As I was putting them back in their boxes, I noticed the values printed on the boxes. All six have GM 6,000 printed on them; 4 of the boxes are labeled Ip 44, and two of the boxes are labeled Ip 55. Is that what my problem was? Did they give me a matching quad, and then add a matched pair that doesn't match the first quad?

I don't know enough about electronics and tubes to go accusing the guy, but that sure is what it looks like to me.

I guess my question wasn't so quick after all!

Thanks in advance!

[johnallg]

Yes, you did not get a sextet of matched tubes, but a quad and a pair. The bias LED circuit is a comparator circuit that needs 6 monitored point to be within the window of the design (value determined by the bias current of the tubes) and with the 11 ma difference in the pair would not satisfy the circuit. The circuit works fine and great as designed, as long as all 6 tubes are colse in parameters. With his logic, how would you ever know if there was a real problem? Since the tubes are in the power circuit in pairs, it was okay to have the sets as he had them, but you would never know if there was a problem. Modifying the circuit or disabling it would serve no purpose except to extinguish the LEDs with the tubes he used.

Personally, I would reconsider using his services again.

[jps]

Personally, I would reconsider using his services again.

+1.

[rickaddict]

Thanks, John. That's what I figured.

I've had the WORST luck with repair people. Where have all the good ones gone? It's like a dying art or something. It's no wonder we live in a throw away society. It's just easier.

I could tell stories about other repair shop nightmares: My old Cerwin-Vega bass amp (it was a super reliable amp for over 20 years before this) spent over 1 year in an incompetent shop...excuses, delays, lies, and then the faulty power switch that caused the problem in the first place was not replaced as I had asked...my Philips stereo receiver (2 tries to fix it at 2 different shops, and I finally just gave up and threw it away)...my motorcycle (carbs rebuilt, but they weren't the problem; the problem is still there, but now my newly rebuilt carbs don't run as well as they did before the rebuild)...and I have countless automotive repair shop nightmare stories as well.

Is this just in Chicago, or has anyone else noticed it?

Maybe I'm just more observant and more picky than most?

Or maybe I have "sucker" written on my forehead!

[jps]

My friend and RRF member, Warren (Full Cleveland), could have fixed your stereo!

[johnallg]

Thanks, John. That's what I figured.

.........

Is this just in Chicago, or has anyone else noticed it?

..........

Or maybe I have "sucker" written on my forehead!

Your welcome Jeff.

Unfortunately, I believe it is becoming more and more prevalent. Way too many ideas why to post here. And yes, you have sucker written on your forehead!

Sorry, I couldn't resist.