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the CTH (Compact Tube Hybrid) Rev A thread... - Page 37

post #541 of 572

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.

post #542 of 572

^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.

post #543 of 572

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. 

post #544 of 572
Quote:
Originally Posted by gurubhai View Post

^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.

 

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.

post #545 of 572

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.

post #546 of 572
Quote:
Originally Posted by gurubhai View Post

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.

 

What's your AC voltage?

post #547 of 572

getting 23.8 vac out of the adapter .

post #548 of 572
Quote:
Originally Posted by gurubhai View Post

getting 23.8 vac out of the adapter .

 

I just looked at the schematics.  It looks like a 2.5x multiplier, which should land it around 85V.  I can't recall what mine is at.  I'll have to take a measure some time later in the week.

post #549 of 572
Quote:
Originally Posted by gurubhai View Post

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.

 

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.

post #550 of 572
Quote:
Originally Posted by KimLaroux View Post

 

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.


R3L = 3.6 V

R3R = 3.48V

 

CRD is semitec E-202 and the tube is a 12fq7.

post #551 of 572
Quote:
Originally Posted by gurubhai View Post

CRD is semitec E-202 and the tube is a 12fq7.
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.
post #552 of 572

I tried both ECC82 and E88C as well. Same issue, infact the clipping was worst with e88cc.

I think it might be a wallwart issue, will change it and report back.

post #553 of 572
Quote:
Originally Posted by gurubhai View Post

getting 23.8 vac out of the adapter .

 

Quote:
Originally Posted by gurubhai View Post

I tried both ECC82 and E88C as well. Same issue, infact the clipping was worst with e88cc.

I think it might be a wallwart issue, will change it and report back.

 

You're probably right.  It is a bit low, unloaded.  I can check mine, if I can find it. :P

post #554 of 572

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.


Edited by holland - 7/2/13 at 7:16am
post #555 of 572

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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