BeePre Finished! Questions about operating temps - tubes and heatsinks

[ewingfox]

Hello!

With a few other builds mid-way when the BeePree arrived (fantastically packed, all parts intact and as always - supplied with FANTASTIC documentation!!)  it has been a few weeks before I could jump into it with both feet.

After a few easy evenings of soldering the preamp is done, passed the smoke test (phew!) and all the voltages are good (a few percent higher across the board, but I run higher than 115v by a few ticks most days here at the house).

SO - the smaller 8907 tubes are pretty hot to the touch - the heatsinks on the rectifiers are too (which makes sense of course) but are there some general guidelines about desired operating temps?  I have an optical thermometer I use frequently with other projects, but a quick search of the forum and I couldn't find this one asked or answered.

I'm sure I'm being paranoid, but I'd rather not have to order new tubes or damage the rectifiers by not double checking. 

One deviation from the measured specs is that on pins C4 and D4 (marked N/A on the voltage check) I'm seeing 6V.  This makes sense based on the fact that these are the neg LV taps off the transformers, but I'd hate to omit a possible cause for concern.

Thank you in advance for any guidance,


Ewing

[Paul Birkeland]

SO - the smaller 8907 tubes are pretty hot to the touch

If you're speaking of the 300B's or EL84's, they will be too hot to touch, as will just about every other vacuum tube in every other piece of tube equipment in existence (except for the 3S4 in the Quickie). 

are there some general guidelines about desired operating temps?  I have an optical thermometer I use frequently with other projects, but a quick search of the forum and I couldn't find this one asked or answered.

Optical thermometers are inconsistent due to issues with how different materials emit IR radiation.  Use of a thermocouple to measure how hot a component is running is the only accurate way to obtain this measurement.  From a paranoia standpoint, if you passed your voltage check and your transistors are mounted snugly to their heatsinks, then your thermal loads will be properly heatsunk.

One deviation from the measured specs is that on pins C4 and D4 (marked N/A on the voltage check) I'm seeing 6V.  This makes sense based on the fact that these are the neg LV taps off the transformers, but I'd hate to omit a possible cause for concern.

C4 and D4 are both pin 4 on the 9 pin socket.  These are not connected to anything.

[ewingfox]

After an hour of sustained listening, the chassis plate was also pretty hot - please excuse my ignorance, my only tube experience with preamps is limited to the foreplay and quickie! Is that to be expected as well?

Sonically - ohmy - I'll need a longer listening session to really have anything meaningful to say.  Anyone who has heard the BeePree knows what it sounds like, and anyone who hasn't heard it - well my first impressions (amazing!) Wouldn't do it justice!

[Rocketman248]

I've got quite a few different Bottlehead amps, and the BeePre is definitely the hottest one.  Just make sure it's well ventilated.  It sounds great, and is pretty helpful on cold days!

[Paul Birkeland]

When you have six 10W resistors underneath a piece of aluminum, plus several toasty tubes and power transformers, the aluminum will get hot. Again, if the voltages in the preamp match those specified in the manual and the transistors and mounted snugly to their heatsinks, the heat is completely normal. 

[ewingfox]

That makes me feel better to hear - I'm listening to bitches brew in dsf and hearing so much more detail - while being incredible musical!