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the CTH (Compact Tube Hybrid) Rev A thread...
Jun 25, 2013 at 3:05 PM Post #541 of 607
It should work, IIRC I used a ferrite core coil like that for L2H in one of my builds & had no issue with it.
The spec'd air core toroid is a "better" part (e.g. lower DCR), but I still say try it.
 
Jul 1, 2013 at 8:37 AM Post #542 of 607
^Thanks.
 
Finished my CTH build and it seems to be working fine except that I am getting some clipping/distortion if I crank it up.The TB+ is about 86V instead of the suggested 95-105V and the pin 1 & 6 of the tubes measure around 79.5V.
I double checked the PS caps and diodes and they are all correctly oriented. Any suggestions would be appreciated.
 
Jul 1, 2013 at 11:05 AM Post #543 of 607
I had a similar problem with my MSSH recently. Turns out the plate current was so low, there was not enough voltage drop across the cathode resistor. This made the grid so close to ground, any input voltage exceeding it made the tube clip and distort.
 
Check what voltage you get at Vk (across the cathode resistor). It's supposed to be around 2.4V. 
 
Jul 1, 2013 at 11:11 AM Post #544 of 607
Quote:
gurubhai said:
^Thanks.
 
Finished my CTH build and it seems to be working fine except that I am getting some clipping/distortion if I crank it up.The TB+ is about 86V instead of the suggested 95-105V and the pin 1 & 6 of the tubes measure around 79.5V.
I double checked the PS caps and diodes and they are all correctly oriented. Any suggestions would be appreciated.
Click to expand...

 
TB+ is with or without the tube?  Try without the tube first.  Also measure the AC coming in without the tube.  Then do the same with the tube.  If it's fine without the tube, your transformer may have problems handling the load.
 
If it is the same voltage without the tube as it is with the tube, it's the multiplier, check the diodes and caps again.
 
Jul 1, 2013 at 5:52 PM Post #549 of 607
Quote:
gurubhai said:
TB+ is the same both with and without the tube at around 85-86V.
 
I checked the transistors and diodes of the multiplier and they seem to be okay and the cap orientation is correct. No loose joint either.
Click to expand...

 
Seems like the tubes are not even loading the rail. Have you checked that the CCS is working correctly? It's easy to verify, just check the voltage across the cathode resistor. It should be around 2.4 V. I'm guessing it's not.
 
Jul 2, 2013 at 9:19 AM Post #551 of 607
gurubhai said:
CRD is semitec E-202 and the tube is a 12fq7.
Click to expand...

Haven't looked at your CRD specs compared to spec'd BUT I'm unsure of that tube.
Years ago we started enumerating compatible tubes (see CTH info in my sig and
http://www.head-fi.org/t/398839/a-very-compact-hybrid-amp/2025#post_6785071)
And that tube is not green/tested/recommended, so could you please try a sure-thing tube like a 12au7 (or other in my typed compatible list) and report back.
 
Jul 2, 2013 at 9:56 AM Post #554 of 607
27.3vac unloaded.
 
BTW, I've used 12FQ7.  I thought it was good.  I currently have a 6GU7 set aside for the CTH.
 
Edit: My heater is not stock.  I reworked it for more current.  I can't recall the original specs.
 
Jul 7, 2013 at 3:15 AM Post #555 of 607
Followup : Connected a 24V/ 2A transformer and the TB+ is now 95.9V. Currently have a BEL ECC82 plugged in listening to a T50RP, no clipping and its whisper quiet. Sounds pretty darned good too.
smile_phones.gif

Thanks for the help guys.
 
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