Dynaco MK II sounds flat after upgrade

Hello.

I recently updated my Dynaco Mk III with
6SN7 OCTAL DRIVER board
SDS Labs Cap Board

The tubes are not new and are old GE Kt88
Old GZ34 rectifiers

Warm up the amps, run some music through them. Completely flat no soundstage no bottom end. No dynamics. Seem like my top end is muted as well. My Bryston 3B runs better.

Any suggestions.. Im gonna guess replace tubes and rectifier and try again. but thats a 300$ gamble.

All items were installed correctly.
All functions as it should ..
Testing was on a pair of Kef 103/4 speakers 4 ohm. low impedance 89db.. this should only affect volume but not dynamics or soundstage.

I had far higher hopes for the units.

They arrived partially unassembled so prior testing and comparing was not possible.


Compared against my Dynaco ST70 and the ST70 sounds better. Not amazingly better but better. More full, better top end, still a little flat. Newer tubes and rectifier. mostly original ST70, no mods.

Any suggestions or comments welcome.

If i can't get the sound out of these i want I'm gonna ditch the MK III and buy a Class A Krell.

Is worth mentioning just hooked up to a pair of early series Klipsch Cornwalls and the MK III sound was not that bad. I may have been over anxious and not thinking when hookin up to the Kef 103.4. Probably not the best match for Tube gear.

I will run them a bit to break in the electronics and possibly order new tubes and report back and compare to the ST70 which is pretty much unmodified.

thanks

Zipper,
Assume you mean GEC KT-88s, not GE KT-88s? The original GEC's in good condition are worth a king's ransom.
Before you go tearing your hair out, could you describe what 6SN7s you're using? The drivers have a far greater influence on sound than the output tubes.
You might also have an impedance mis-match as well between the MK and the pre-amp.
Don't go tossing those GEC KT-88s. I'll be glad to take them off your hands, as would most any member of the forum. I will even pay postage.
Cheerio,
deepee

KT88's are Westinghouse Premium G&C KT88 tubes. Made in UK.
I have 4. one seems bad but i am waiting to get them tested this week. I have (2) General Electric 6550A
One Dynaco MK III runs 2 G&C the other runs one G&C and GE 6550A
(just realized this is probably not good. but this is the diagram by the PO how it was operating so i matched it. Re-biased and runs.)

The pre tubes are bran new and came with the new Octal board from tubes4hifi and they each run (2) 12au7 Electro Harmonix
http://www.tubes4hifi.com/MK3.htm

Also installed this
http://www.triodeelectronics.com/sdslabmk3cap1.html


One rectifier is Dynaco original says Dynaco on it. The other has no identifiable markings on it at all.

The preamplifier is a Bryston .4B


Thank you for ur help.


PS>>And i appreciate your honesty about the value of the tubes. Im the same way in other forums where i know more. I am still learning about Tubes.

zipper wrote:KT88's are Westinghouse Premium G&C KT88 tubes. Made in UK.
I have 4. one seems bad but i am waiting to get them tested this week. I have (2) General Electric 6550A
One Dynaco MK III runs 2 G&C the other runs one G&C and GE 6550A
(just realized this is probably not good. but this is the diagram by the PO how it was operating so i matched it. Re-biased and runs.)

The pre tubes are bran new and came with the new Octal board from tubes4hifi and they each run (2) 12au7 Electro Harmonix
http://www.tubes4hifi.com/MK3.htm

Also installed this
http://www.triodeelectronics.com/sdslabmk3cap1.html


One rectifier is Dynaco original says Dynaco on it. The other has no identifiable markings on it at all.

The preamplifier is a Bryston .4B


Thank you for ur help.


PS>>And i appreciate your honesty about the value of the tubes.  Im the same way in other forums where i know more. I am still learning about Tubes.

Install NEW tubes and enjoy the music. If the old kt88 is so valuable, then sell them.

in europe JJ 6550 is a good candidate, on pair with jj kt88 but 30% lower price. In
US i suppose EH is the logical choice.

Old power tubes affects more then one thinks. They are consumables, so don't hesitate to
replace them.

"The pre tubes are bran new and came with the new Octal board from tubes4hifi and they each run (2) 12au7 Electro Harmonix"

This is confusing because an octal driver board takes 6SN7s not 12AU7s. You must have the standard VTA board ???

Yes the VTA board. The Octal is for the ST70 my bad.

VTA with 12AU7

Kentley, he's talking about the AU7s in his pre-amp, not the octal driver board. You can't fit a noval tube into an octal hole.
Question remains, Zipper, what brand of 6SN7s are you using on the octal driver board? If they are newly-made Russian Tung-Sols they need several dozen hours' burn-in time. I have other preferences but will not go into that here.
Peterh is absolutely correct in that a near-to-fail output tube will adversely affect the sound and when it finally goes pear-shaped may take some other parts both downstream and upstream with it. Any easy test of its health is, does it hold correct bias or has it started wandering around? If it goes out of range to the high side, donate it to charity.
I have no experience with the JJ 6550s Peterh recommends, but having run original Tung-Sol 6550s of early 1960s vintage (as well as GE 6550As, which I found quite flat, and several Russian versions of the 6550), I finally sold all of my 6550s and am quite content with the Russian-made Genelex Gold Lion KT-88s. A sturdy output tube and very elegant sounding. If you go the Gold Lion route, Jim McShane at mcshanedesign.net would be my recommendation. Jim puts them through some real-world torture before shipping.

[quote="zipper"]Yes the VTA board. The Octal is for the ST70 my bad.

VTA with 12AU7[/quote
Ah so. Understood.
My decidedly amateur opinion is that you should probably procure a matched set of KT-88. A lot of forum folk swear by the new Genalex, and the Sovteks seem solid as well. If you buy new tubes, you owe it to yourself to go through Jim McShane, as he is rigorous in his selecting and matching. {link below}. I'd also be somewhat wary of Electro Harmonix products. Many of us here have had poor luck with them. They seem to be geared towards the guitar-amp crowd.
Good NOS 12AU7s are not expensive. Probably LESS than new ones, and there's a wide variety out there. Maybe a good place to start is the RCA 5963 which is a ruggedized 12AU7 which can be had on EekBay for $5-10 a shot.

http://www.mcshanedesign.net/tubes.htm

Do your MkII input boards allow individual biasing of the output pair? I'm sure they do otherwise you would not be running an unmatched pair, right?

Another thing you could try is to use the 4 Ohm taps.