trinityamps.com

Since I have made the gain changes in the TMB Chanel it seems the V2 is not surviving thinks it drawing too much, Well going over Richard's original schematic was seeing the added power cap for v1 (splinting the load more or less) . And was wondering if that might help my issue. I recall Kurt saying (asking) about some extra filtration. Was also wondering how much of a dropping resistor to put in before the added cap.

so far this is what I have done
- v1 tmb cathode res 2k7
- tone stack changes
- vrm
- front end v2 470k/390pf/470k and .0068 coupling cap
- 1meg gain pot
- v2 boost original 2k7 with the switched in 1k5 and .68 cap
- screen resister 250R

I don't think it is V2 that is drawing too much. I think it is the phase inverter and power tubes. When I had the EL84s with the PI set to 470R/56K, my PT would really sag a lot. I think it is because the pre-amp signal is too hot for the 18 watt PI/Power design. I had put gain reducing mods in to reduce the gain before the PI as well as changing the PI cathode from 470R to 820R but even then the signal was still a little too hot and the PI was driven too hard and was fizzie. Now with 6CM6s that can take a much hotter signal, I have removed the gain reducing mods and the PI is set to 470R/15K and it sounds great. I also have very little PT sag now.

With the brown mods already producing a lot of gain, 1M pot is too hot. You need to have 500K pot (maybe even lower) as well as maybe some gain reducing mods. You can try adding a 220-470K inline resistor right on the input of each of the gain and master pots VR1 and VR7 to help reduce the signal.

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Les

http://www.soundclick.com/unimind

It seems that V2 gets burnt like its starving ie the silver top changes to black. or if its a darker top to start with it seems to go more black. And I think this is slowly whats taking out the rectifier volume drops over time 12 to 25 hours of use. Could also be the power tubes taking it out. As for the cap side of things was just comparing to other builds ands thinking that with most builds (higher gain) have a split power supply with v1 and v2.

If I used Duncan's power supply calculator correctly it comes up with another 2k2 and 16uf that can be added to supply v1 and v2 plates separately

What I used as a (32uf 80ma pt draw) (1k5 32uf 10 ma screen draw) ( 8k2 16uf 3ma v3) (2k2 16uf 3ma v1) (2k2 16uf 3ma v1) unless my curent draw numbers are too low or I missed something.

V2 is a cathode follower.

The cathode follower puts a very high voltage on the cathode (your probably seeing somewhere between 180V-210V). A lot of modern tubes cant take this voltage. The heater to cathode voltage is speced in the data sheet and at a certain voltage (I think its roughly around 200V) many tubes can break down and die.

On many tube retailers websites it even says on certain tubes "don't use this tube in a cathode follower position". This is because these tubes cant take the heater to cathode voltage they are subjected to. Off hand I believe Tung Sols and Mullard reissues have this problem.


That's my guess anyways. Telling us which mods you have won't really help. Ideally we need voltages on the tubes, as well as what kind of tubes, etc.

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http://pdfelectronics.com

Ok I see. I'll have to take a some measurements when I can. But as for voltage the vrm was always running at b+ 300v would that actually put the cathode that high ( will measure) As for tubes i've tried two old mullards and a new jj in v2. as for the others v1 bugle boy. v3 new eh. pair of eh el84's and a jj rectifier.




Is this why I am seeing a lot of elevated heater circuits out there ( thought that was for noise) ?

Often the heater centre tap is connected to a high voltage and that is known as heater elevation.

It's different than what I was mentioning before though.

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http://pdfelectronics.com

Ok looking at the changes I made it might be the fact that I changed the v2 cathode resistor from 56k to 100k. I take a lot a time to mull things over and if I see something go wrong or see some completely different ideas out there I'm always asking why.

And thanks to every one for the for the help.

As for the tonal changes really like where the tmb channel is at now. As for the way it was originally it was ok for me ( not knocking anything) just not my earl gray cup of tea. Could come up with a tone with or without boost just not both imo.

The dark channel was perfect to start with in my taste zone very useful in my playing . So I have dropped the cascade mode ( did try it for a bit) but sound wise was always too dark imo. I wasn't about to start messing with that side.

So when i get done tweaking this mother I was thinkin' maybe a TCM800

b+ vrm fully up 357 v

v2 pin 8 180v boost on 156

B+ vrm normal position i play 290 v

v2 pin 8 154 v boost on 126

Those voltages are almost identical to what I get but I don't have any problems with tubes turning black.

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Les

http://www.soundclick.com/unimind