Scott 299B Issue with Tube?

[Rmac587]

Hi All,
My rebuilt NOSvalves Scott is my baby, but it seems to have an issue. Symptoms:
-the power indicator lamps on front are taking longer to warm up and glow.
-it seems that I have to turn the volume up a bit more to get the same level.
I don’t have a tube tester, but I’m wondering if replacing the rectifier tube might be a probable solution. This may be a bit of wishful thinking and hoping for a simple solution. Any insight from the tube gurus?

 

[Dave451]

Did Craig install a CL-80 in rush current protector in the rebuild? I did in both of mine and it does delay the B+ voltage lighting the panel lights a good bit (but that's a good thing--if you have one, it protects the on/off switch and knocks a couple of volts off the line voltage to the amp, which runs hot anyway!). I didn't detect any difference in volume setting, though, in either case.

As for rectifier tubes, in my experience they either work or they don't with no apparent changes as long as they work. If your output tubes were re-biased in the rebuild, that might affect the output slightly (or if any of the tubes were changed, particularly the output tubes).

Did the issues appear just after the rebuild or some time after the rebuild?
Dave
PS Love the 299B--one of my favorite amps!

 

[Patrice B]

As for rectifier tubes, in my experience they either work or they don't with no apparent changes as long as they work.

I can tell you that I had once a Sovtek 5AR4 with a dead section and it worked, kind of ...but the amp (an Heath AA-100) hummed like crazy!

 

[Dave451]

Interesting, I had the Amperex rectifier 5AR4 fail in my first 299B and, surprisingly, it didn't hum but it wouldn't produce full power. One side didn't light up. I replaced it with a Sovtek and have had no issues since.

 

[Rmac587]

Did Craig install a CL-80 in rush current protector in the rebuild? I did in both of mine and it does delay the B+ voltage lighting the panel lights a good bit (but that's a good thing--if you have one, it protects the on/off switch and knocks a couple of volts off the line voltage to the amp, which runs hot anyway!). I didn't detect any difference in volume setting, though, in either case.

As for rectifier tubes, in my experience they either work or they don't with no apparent changes as long as they work. If your output tubes were re-biased in the rebuild, that might affect the output slightly (or if any of the tubes were changed, particularly the output tubes).

Did the issues appear just after the rebuild or some time after the rebuild?
Dave
PS Love the 299B--one of my favorite amps!

Hi Dave,
I feel pretty certain he did, I’d have to check documentation. I suspect a weak tube somewhere, but have no way to test. I just love the amp though. It seems that a rectifier is an unlikely culprit given the overall comments though. I’ll check the bias, although I already did not too long ago.

 

[FB night]

I have several of the Scott amps, and have worked on many of them. Check the input voltage where the amp is plugged in to. I once sold an amp to a fella, and he complained of the same thing happening, turned out his house had old and poor electrical, and the problem turned out to be low voltage from his power outlet. His problem was in his breaker box. Then I would replace the rectifier tube, see if that is the problem. I think the JJ rectifier tube is only around twenty dollars, does not hurt to have a good spare one of those anyway. Also, check the fuse, I have had fuses half melt, but still sort of work. Make sure it is of the correct type and rating.

 

[Dave451]

Rmac,
The CL-80 will definitely slow the start up of a unit with a rectifier tube--that's perfectly normal. The CL-80 thermistor has a high resistance when cold, which limits current until it warms up and the resistance falls. Then the rectifier tube has to warm up and get going. The CL-80 will knock just about 2 VAC off the line voltage after warmed up, so if your line voltage is already low, it will now be 2VAC lower, per FB night's comment and this could affect output.

So, if there's a CL-80 installed, there's no need to worry about a somewhat delayed startup--it's doing what it's supposed to do. A small change in volume control position after a refresh is not something I'd worry about if the amp sounds right, but it's your amp. It never hurts to check bias on the output tubes and a new rectifier tube can't hurt, but may not make much difference.

If you want to have a more nuanced response, a description of exactly how much the volume control has shifted would help, as would a description of the refresh work done by NOS Valves (were any new tubes installed, for example).
Dave

 

[primosounds]

Hi All,
My rebuilt NOSvalves Scott is my baby, but it seems to have an issue. Symptoms:
-the power indicator lamps on front are taking longer to warm up and glow.
-it seems that I have to turn the volume up a bit more to get the same level.
I don’t have a tube tester, but I’m wondering if replacing the rectifier tube might be a probable solution. This may be a bit of wishful thinking and hoping for a simple solution. Any insight from the tube gurus?

Are these symptoms something that has started recently? If it is something you noticed after the rebuild then i would not be overly worried. But, if you have doubts just open up the bottom and take voltage measurements to find out how they compare with the values given in the owner's manual. If everything checks out then you should be ok.
BTW, if you know that your wall voltage is say close to 117 and less than 120, there is no real need to have the CL and maybe causing a reduction in performance.

 

[Rmac587]

Are these symptoms something that has started recently? If it is something you noticed after the rebuild then i would not be overly worried. But, if you have doubts just open up the bottom and take voltage measurements to find out how they compare with the values given in the owner's manual. If everything checks out then you should be ok.
BTW, if you know that your wall voltage is say close to 117 and less than 120, there is no real need to have the CL and maybe causing a reduction in performance.

Now that I think of it, it may be that we are getting a slight “brown out” decrease in power due to hot weather. It sounds fine however.

 

[primosounds]

If you can check the AC wall voltage to your amp at the time of your listening. That would give you a clear idea of what is going on with your primary voltage and maybe it is affecting the power output of the 299.