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Hi, this is my first post. I have built the ST35 and now the eiclone. I am very happy with both. My question is how to wire the eiclone board for triode operation. I have wired a Dynaco ST70 for triode and it made a huge difference. I am using KT88's in my eiclone and I think triode would be a benefit. Any advise would be appreciated.

The usual approach would be to disconnect the UL taps of the output trannie's Screen Grids, (cover the ends of the UL wires for safety), and then connect a 1K 2W resistor between the plate and UL connections on each of the two the terminal blocks. This leaves the option of returning to UL operation at a later time, if desired, and doesn't involve any PC board surgery. No soldering required.

A more elegant approach would be to install a good quality DPDT toggle switch, and make the triode or UL modes switchable. The caveats here are to be sure that the switch can handle the high DC voltage, and to never switch modes when the amp is powered up, this can do bad things to the KT88s. VTL uses this approach, and offers the same warnings about flipping the switch with the power on.

/ed B in NH

golnie wrote:Hi, this is my first post. I have built the ST35 and now the eiclone. I am very happy with both. My question is how to wire the eiclone board for triode operation. I have wired a Dynaco ST70 for triode and it made a huge difference. I am using KT88's in my eiclone and I think triode would be a benefit. Any advise would be appreciated.

WES - What Ed said.

BTW, the Ike's are full of undocumented features. R25 and R26 are footprints for triode strapping resistors if you choose a more permanent solution. Even if just for a temporary test you can disconnect the UL taps, insulate them somehow, and 'surface mount' your 1K resistor on R25 & R26. 'Course it's probably just easier to 'surface mount' on the socket pads 3 & 4. Easily reversible if you miss the power.

Also, R44 and R45 are jumpered screen resistors. To use these, cut the trace shorting them and drop in a screen resistor - once again, a 1K, 2W one would probably work well. That said, I've yet to do any tests with screen resistors. It would be interesting to see if any stability or performance is gained at high output. My guess is better stability and worse distortion. I hate to tinker with ultralinear.

Shannon

I have read totally differing and oppsing opinions on the subject of using resistors on the screen grids in an UL curcuit, there are those who state that resistors of 100 -1K ohms are absolutely necessary, and those who state that the connection should be direct fron SG to UL tap.


I've tried both ways, never really found any discernable difference.


I'll try boosting the bias up to 65-70 mA with the 6550Cs and see how it sounds...

/ed

Many thanks to Mr Brown and Mr Parks for their help. I did triode wire by jumping the UL terminal with a 1k resistor. It did smooth out the edge of the KT88's. Though it is hard to tell what you are hearing and what you want to hear. BTW I had a quad of KT66's (valve art) that I tried and honestly I prefer them to the KT88's.

Thanks to EWB for the following, I have read it about 5 times now, along with the ultra-linear one.

http://www.webace.com.au/~electron/tubes/screens.htm

Don

I have some Saratov KT66s I was thinking of trying out as well as the Svet 6550Cs.

/ed B in NH