So I'm wondering if adding a fan is beneficial. I have Acoustat X Direct Drive Servo mono otl amps. They are always on but on standby til they receive signal. It seems sq peaks after about 5 songs and then drops off but very slightly, I'm actually not quite sure. Sound is a bit less crisp/up front sort of. Maybe it's just in my head? Maybe line voltage? It's 122v here.
Noctua makes very good and quiet fans. But personally, keeping tube gear on standby is a waste of tubes and electricity.
Right, but what do you think about the change in sq? Could my assessment have merit iyo?
Yea, the amps are built that way. Could there be a power surge issue if I installed a switch?
Yea, the amps are built that way. Could there be a power surge issue if I installed a switch?
Most of the time I see no point to fan-cooling tubes in audio amps. They get rid of most of their heat through infrared radiation, not through conduction.
Where fan cooling makes sense is with external anode tubes (which are silly for audio applications) or tubes that require airflow over the glass-to-metal seals. The other application would be if you're really pushing plate dissipation in a confined area and you're worried about cooling the seals, or you're worried about cooling other parts in the amplifier.
FWIW (because people get strange ideas that make no sense), the temperature of the glass-to-metal seals will have absolutely no effect on the performance of an audio amplifier. Where it's an issue is when those seals overheat and get leaky. The tube gets gassy, turns purple, blows up, etc. This is mostly an issue with high-power RF tubes like 4-125As, 3-500Zs, etc.
I can't explain the sound quality change you are hearing, but I do not believe it is related to the temperature of the tubes. It would be more useful to try to quantify it (distortion, frequency response, etc), otherwise you're just chasing your tail.
Where fan cooling makes sense is with external anode tubes (which are silly for audio applications) or tubes that require airflow over the glass-to-metal seals. The other application would be if you're really pushing plate dissipation in a confined area and you're worried about cooling the seals, or you're worried about cooling other parts in the amplifier.
FWIW (because people get strange ideas that make no sense), the temperature of the glass-to-metal seals will have absolutely no effect on the performance of an audio amplifier. Where it's an issue is when those seals overheat and get leaky. The tube gets gassy, turns purple, blows up, etc. This is mostly an issue with high-power RF tubes like 4-125As, 3-500Zs, etc.
I can't explain the sound quality change you are hearing, but I do not believe it is related to the temperature of the tubes. It would be more useful to try to quantify it (distortion, frequency response, etc), otherwise you're just chasing your tail.
Yes they are in great shape. I'm using 4 and they all sound the same. I hear the same thing when I use ss amps. Hence my suggestion it's all in my head.🙂
Fans on a tube amp are better used cooling the power transformer than the tubes. Tubes are designed for the heat to function as long as they are within the design specs. Power transformers are happier when not overheated, they last longer and the radiant heat will be less if fan cooled.
I can't say if it's a psychological issue or physiological issue, but I can, with reasonable confidence, say that it's not a hardware issue.
I use fan-cooling on my H.H. Scott 299 tube amp, the reason being that it's a crowded chassis and has the rectifier tube mounted too close to the filter capacitors, in addition to Scott's often-used technique of providing some shunt-regulation of the 7189 screens via large wirewound resistors that get very hot. I got a SilenX computer fan and hung it blowing across the amp. It's powered by a small DC power supply plugged into the amp's switched outlet. It runs at lower-than-full voltage, so it's not audible.
If you want to use a fan, get a large one. Larger fans turning slowly are better for noise than a small fan running fast.
Pretty much every unrestored 299 will have a shorted filter cap and a shorted rectifier tube.
If you want to use a fan, get a large one. Larger fans turning slowly are better for noise than a small fan running fast.
Pretty much every unrestored 299 will have a shorted filter cap and a shorted rectifier tube.
I used to have those, 20+ years ago. Played with them too - had the TV anode probe to measure the B+, which I even bypassed with these giant oil caps that sat on the floor behind them. Changed out the quad op-amp too. Lived to write this! When my baby boy started toddlin' I got rid of the amps and later the speakers - hard to drive w/o them via their std box. I dont recall having the cages with the power cord interlock, which is probably "why". They sure drove the Acoustats plenty loud. Some of the passive components used on that PCB are just fascinating, especially the big red output caps. I remember marveling at the anode voltage those 6HB5 TV tubes they used could take. I think B+ was 4.5 kV...
I see on the web someone has a mod where they get rid of (apparently) the quad op-amp and replace it with a long PCB with 3 signal tubes...
Yea, I saw that mod. Mine have the standard poly cap mods and opamp upgrades. The servo is really what they need over the interface to bring them alive. Completely different speaker that way. Contrary to popular belief they are actually very reliable. I've had one tube fail among 4 amps over the years without consequence to other components.
Not in the case of the Acoustat amps as this keeps the amps alive (moisture is deadly for these amps as dust will accumulate and bond with it over time creating a resistive layer on the PCB).
That's just bad design if this one amp requires that when others get by without it. Had the designer never heard of conformal coatings?
Standby is wasteful of electricity and tube/component life.
Standby is wasteful of electricity and tube/component life.
What others? There was no other... who else was building 5KV amplifiers?
After 40 years many of these amps are still in use ! Only the ones that have been modified (removal of the stand-by circuit) and those that have been switched off are dead for the reasons mentioned.
After 40 years many of these amps are still in use ! Only the ones that have been modified (removal of the stand-by circuit) and those that have been switched off are dead for the reasons mentioned.
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