Cavalli Compact Tube Hybrid (CTH) Tube & Tweak thread. - Page 43

Quote:

Originally Posted by Tribbs 

Quote:

I'm game, Sachu.  But I'm unfamiliar... Would someone be so kind as to provide the Belleson reg. part# or link, please? - TIA.
 

 

http://www.belleson.com/order.php

Select High Current 2.0A.

YOu want the SPJ78 in 24V configuration. 

THis will be a far better thing to do than investing in a 6F8G or any exotic tube IMO.

Quote:

Originally Posted by runeight 

Remove one lead of R10E. Replace Q1S and Q2S. Replace Q3S, Q5S, R5S, R7S.

 

Make sure that the Vg point is not actually grounded anywhere.

 

Then try again. This may take a while.

Thank you for your kind help.

Yesterday I removed Q5S and Q3S (both were barbequed) and I measured the expected +12V at VG (without IC1 inserted). Nothing was heated up. R5S, R7S have survied, but I will repace them.

But the measures are different for the R and L output buffers, so one of them must be wrong:

• L buffer: +24V at the base of Q8L, +23V at the base of Q9L, 22.3V at the base of Q4L-Q5L
• R buffer: 0V at the base of Q8R, +4.4V at the base of Q9R, 0V at the base of Q4L-Q5L

D2L, D2R, Q8L and Q8R are not damaged.

- That was measured without IC1 inserted, and with the absence of Q3S, Q5S at the splitter. (I am afraid that they may be damaged again if I do not solve the problem at the buffers)

It was too late at night for thinking clearly. I will continue this evening.

Conclusion 1: I need glasses. This weekend I will go to the optician

Conclusion 2: I miss my desoldering iron (the one with the pump attached into the head). Here in Thailand I can only find that sucker tube with a spring, and it is devastating for the small PCB of the CTH. Everytime that the spring is released, it spits mico-particles of soldering that are spread around the board. And it does not seem to work with double sided PCB's. I had to cut the transistor pins with cutting pliers (fortunately I let them very long) and then remove the pins one by one.

Update:  Q4R was completely shortcircuited between e-b-c in all directions (zero Ohms!) This is what made all voltages to drop at the Right Buffer.

I am wondering what could cause Q4R to die like this. DC from B+ passing through C4R?

Q5R, Q6R and Q7R seem to be OK. I have not removed them, but the diode-test readings are identical than at the Left Buffer.

Quote:

Originally Posted by sachu 

http://www.belleson.com/order.php

 

Select High Current 2.0A.

 

YOu want the SPJ78 in 24V configuration. 

 

THis will be a far better thing to do than investing in a 6F8G or any exotic tube IMO.

Ouch - for nearly $70 shipped it should be very exotic indeed -  rich!

@sachu So what is this tweak going to do for this amp? Less hum for 32ohm in ear phones?

What he said ^

I noted the physical dimensions are 0.5" (12.7mm) Wide x 1.85" (38mm) Tall

Is there enough headroom to fit it into the standard size Hammond case?

Did you change any related capacitors?

Quote:

Originally Posted by Pingfloid 

Update:  Q4R was completely shortcircuited between e-b-c in all directions (zero Ohms!) This is what made all voltages to drop at the Right Buffer.

 

I am wondering what could cause Q4R to die like this. DC from B+ passing through C4R?

Q5R, Q6R and Q7R seem to be OK. I have not removed them, but the diode-test readings are identical than at the Left Buffer.

Was Q4R the right transistor type?

Quote:

Originally Posted by Tribbs 

What he said ^

 

I noted the physical dimensions are 0.5" (12.7mm) Wide x 1.85" (38mm) Tall

 

Is there enough headroom to fit it into the standard size Hammond case?

 

Did you change any related capacitors?

It's actually 1.25" (32mm) tall according to the pdf.  Looks like a potentially tricky installation with the Hammond case.

** edit: Using a toothpick into a vent hole I measure ~33mm between the top of the pcb and the top exterior of the Hammond case.  Subtract 1-2mm for lid thickness. **

Has anyone tried one in a CTH yet?

BK

Quote:

Originally Posted by runeight 

Was Q4R the right transistor type?

 

Yes. But I am thinking of a possible cause of the meltdown: In order to test different caps, I have clips on C4L, C4R. I have been very careful to ensure that the leads have not touched each other while applying power, but when there is no tube inserted into the circuit, B+ remains around 50~58V for several minutes after power is switched off. Perhaps C4R was short-circuited when I put the CTH back into the drawer. The maximum collector-base voltage for the BC560 is 50V.

After replacing Q4R, the voltage below D2R still drops from +24V to 0V. There are no short-circuits; all the ohm/diode readings are almost identical in the main points at both L/R circuits; I have swapped D2L/D2R; but so far I have not been able to find other damaged component on the Right Channel Buffer. All that test are done without IC1 inserted into the circuit..

EDIT:

Runeight, you are my hero! The original Q4R was a 560, but I replaced it for a 550. I didn't noticed until I watched it with a big magnifying glass. The numbers are difficult to read and I still haven't gone to the optician...

Now it's working!!!

Thank You very much to all of you that have made this project possible.

pingfloid, does this mean that the amp is making music now?

Quote:

Originally Posted by runeight 

pingfloid, does this mean that the amp is making music now?

YEAH! Beautiful music in 3D   I have only played it for a little time, but as a first impression I have to say that I am surprised with the wide soundstage.

Thank You very much for your kind assistance, and thanks to all the persons that have ben involved in the design and support of this great little amp.

Ah, good news then. Happy listening.

This amp is literally HOT.

• Center of ICP: 83 degC
• Top of ICP heat-sink:  100 degC
• Most transistors: from 62 to 71 degC

Even far away from ICP:

• Q1E, Q2E, Q3E: 71 degC

One of the coolest part is the tube, with 63 degC.

Measured with a Fluke 62 Mini IR Thermometer, after 40 minutes of work, in a air conditioned room at 24 degC. Hammond case with the cover removed.

In my house, with the room above 30 degC, it is much hotter than that. I will measure it tonight.