Tubes and cats

[Mmaxed]

Be careful using these website high frequency hearing testers (in assuming you get a accurate result).

Or just have your 21 year old son 2 rooms away asking "Anyone else hear that high pitched whine?"  while you're trying to hear the 14k tone sitting right in front of the computer speakers.

[STURMJ]

lol
There is a new piece of gear here at work, the yonsters cringe during a certain function. I hear somthing but its not annoying.  and others hear nothing.  I used a spectral analyzer (on a samsung 10.1 for what that is worth)  and there is about a 90dB spike at 18k. I tell the youngsters that they won't be hearing that for long.

[Grainger49]

I worked at a stereo shop in my late 20s that used ultra sonic motion detectors.  The frequency was 19,500 Hz.  Fred Pinkerton would come in, unlock the shop and start cleaning up.  I'd come in and all but be knocked to my knees.  It would shake my fillings out.

Then Fred would look at me and say, "Oh, I left the motion detectors on again, didn't I?"

Those days are long gone.

[Doc B.]

They had those in my high school. I had to avoid certain stairwells where they seemed to always leave them on. I sure couldn't hear them today. My top end dimished after many years working in front of commercial ovens. The fan noise isn't that loud, but it's constant and I suspect it contributed to a loss above 14K I noticed when I was in my late 30s.

A lot of guys in the audio industry will refuse to admit to that top end loss. Unfortunately for them I happen to keep test tone tapes around. "Yeah, that's 15K. Yes it's playing, look at the meter."

[RayP]

Back to the vomit and yes, the cat is still alive.

I've just got a 6E5P - 6C33C parafeed amp going and I think I have it sufficiently cat proofed.

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi87.photobucket.com%2Falbums%2Fk125%2Frperry13%2F001_zps30359311.jpg&hash=394803242b488403b45c3edae49c1d9308586534)

The wire trays came from Ikea I think and I have cut out some holes for the 6C33Cs which are mounted above the plywood top to help dissipate the heat. I am using a 100 watt 1k resistor as plate load for each channel so that is mounted on top between the two output tubes. The 400 ohm bias resistors are mounted on the aluminium plates. There is not too much heat producing stuff under the top board. The output transformers are THP-60 Tannoy line transformers that can be configured as 650 : 8.

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi87.photobucket.com%2Falbums%2Fk125%2Frperry13%2F002_zps4bdd1c95.jpg&hash=b9695defba95d30ed58c7fdd4df421f430b136eb)

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi87.photobucket.com%2Falbums%2Fk125%2Frperry13%2F005_zpsff3f4c51.jpg&hash=5d9ff75711d3f549f87cf25298efb3a9e0969983)

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi87.photobucket.com%2Falbums%2Fk125%2Frperry13%2F004_zps91f6c2a1.jpg&hash=5d1f68a1e03e5bc3db2c5df0630fc4a7968f53c8)

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi87.photobucket.com%2Falbums%2Fk125%2Frperry13%2F003_zps3db26d24.jpg&hash=8f5ca964fcb65c842c1b9134b4d3e55fefb97930)

I've never tried these tubes before so I have not done anything too fancy such as fixed bias. Surprisingly when I eventually got it working the voltages were within a couple of volts of what I expected. Naturally they have moved a little but it all appears to be stable now. It's a pretty decent amp and hopefully it will work when we hold our next Bottleneck meet which we think will be on one of the last weekends in February depending on the weather.

Getting back to the cat. She hopped up to take a look and you could almost see her thinking 'What the hell is this?'. She sniffed a little and went to sit on the laptop which is my music server.

ray

[Grainger49]

Awesome.  Some years back I bought a pair and, it seems, two pair of sockets.  Using them in SET Parafeed seems perfect.

PB has fooled around with them too.  His avatar (I think it is current) shows the amp.

[Paul Birkeland]

Holy cow, are you running 800mA per tube?

[RayP]

Good lord no! I'm running the standard 200 volts, 200 ma with a bias of 80 volts. Since I had read that the 6C33C is somewhat variable, I decided to put two permanent meters for each channel's bias as well as one for B+ so that I could monitor what the voltages were on a regular basis.

The photo shows one of the bias meters with the reading of 80 indicating roughly 80 volts. The meter is a 1 ma meter

http://www.allelectronics.com/make-a-store/item/pmd-1ma/1-ma-dc-panel-meter/1.html

For the bias meters I hook them up with a 100K resistor between the meter and the cathode of the 6C33C and the other side of the meter connects to ground. For the B+ I use the same meter but with a string of resistors that add up to 1 meg. I allow 100 to 150 volts for each resistor so in this case I just have five 200k resistors. The B+ meter reads approximately 48.

B+ is 480.
The drop over the 1K resistor is 200.
The drop over the plate is 200.
The bias is 80.

I apologize for the confusion.

ray

[Paul Birkeland]

Ah, whew, I saw that ammeter and just had to ask!

I run mine at about the same operating point, though I think it's something like 210V/250mA.

A lot of forum posts discuss how inconsistently these tubes bias, and how variable the idle current is, but this has been far from what I've observed.  At 250mA, I might see the bias wander by 1/2 a mA one way or the other. 

If you are enjoying the amp, the Magnequest BAPC is a nice load for a 6C33 parafeed. 

-PB

[RayP]

Thanks for the suggestion. What do you use as your output transformer?

ray

[Paul Birkeland]

I use the Magnequest EXO-800. 

-PB

[roscoe primrose]

Cats are easily replaceable

Roscoe