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6T9 valve RCAs and GEs
http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=97
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Author:  mwhouston [ 04 Sep 2008, 17:01 ]
Post subject:  Re: 6T9 valve RCAs and GEs

gmilitano wrote:
billnchristy wrote:
I am really interested in the UL mod. I know it sounds easy but I need to see it...I am that kinda guy. Did you put a switch in so you can run either way?

Hi Bill. Mark gave me this project a while back but I have been busy. I will get the UL Conversion page up tonight.

Yes, you can use a switch. Alex used a switch on his Single Ended KT88 Tube Amp. For even more flexibility, I would put a switch on the NFB so you can turn that on and off too.

Guys you are right, a switch to switch Pentode/UL and a NFB/0NFB switch, as Gio has said, would give this little amp a lot of flexibility. My valve monoblocs not only allow power valve exchange but Pentode/Triode mode switching too. You can lose a Saturday afternoon in combinations. And I've found some beaties!

I found the 6T9 was better in UL mode rather than Pentode mode. The music just got better.

Author:  mwhouston [ 04 Sep 2008, 17:12 ]
Post subject:  Re: 6T9 valve RCAs and GEs

billnchristy wrote:
Another couple of questions:

1) all non-listed resistor values are 1/2w correct? (edit, actually they look like 1/4?)
2) Snubbing is the same as bypassing no? basically just a small cap around the big cap?

I am working on a parts list sheet like I did with the 24v aikido, I will post it when it is finished.

I think Gio is right 1/4W resistors. And yes snubbing is the same as bypass, smaller caps around bigger caps. And of course caps on your diodes.

Author:  Gio [ 04 Sep 2008, 20:20 ]
Post subject:  Re: 6T9 valve RCAs and GEs

Ok, here is a link to Mark's Ultra-Linear Modifications for the 6T9 Tube Amplifier Project.

Author:  billnchristy [ 05 Sep 2008, 00:27 ]
Post subject:  Re: 6T9 valve RCAs and GEs

Thanks for the article!! I think I am going P2P on mine to practice for the KT88 build...I have never P2P anything.


In the schematic, between the input and the capacitor...what is the loopy circle thing?

I noticed it yesterday and could not figure it out.

Author:  Gio [ 05 Sep 2008, 07:29 ]
Post subject:  Re: 6T9 valve RCAs and GEs

Hi Bill,

That loop around the input line indicates a shielded wire.

Author:  billnchristy [ 05 Sep 2008, 07:55 ]
Post subject:  Re: 6T9 valve RCAs and GEs

Ahhhhh. Gotcha...do you actually ground the shield?

Author:  billnchristy [ 05 Sep 2008, 08:21 ]
Post subject:  Re: 6T9 valve RCAs and GEs

What do you guys think about putting a pot on the NFB line instead of the 33k resistor?

Author:  Gio [ 05 Sep 2008, 12:01 ]
Post subject:  Re: 6T9 valve RCAs and GEs

Yeah, ground the shield. Depending on your layout a shielded input may not necessarily be required.

A potentiometer? Why not! That is the nice thing about DIY ... custom gear. I'm all for flexibility in audio equipment.

Another option may be to use an opamp socket. Then you can use discrete resistors and change the value.

Author:  billnchristy [ 05 Sep 2008, 13:19 ]
Post subject:  Re: 6T9 valve RCAs and GEs

I've got all my parts ordered but the trannys...anyone know how long it takes Edcor to get back with people? I shot them an email saying what I wanted and told them I would PP the cash as soon as I knew the total...nothing yet. :confused:

I have some zebrawood coming for the chassis with african blackwood legs and a carbon fibre top panel...the chassis cost as much as the amp :eek:

Author:  mwhouston [ 05 Sep 2008, 18:07 ]
Post subject:  Re: 6T9 valve RCAs and GEs

Gio wrote:
Yeah, ground the shield. Depending on your layout a shielded input may not necessarily be required.

A potentiometer? Why not! That is the nice thing about DIY ... custom gear. I'm all for flexibility in audio equipment.

Another option may be to use an opamp socket. Then you can use discrete resistors and change the value.

Generally pots are not used in FB ccts. There may be too much current for the pot and also if the pot is a little noisy you may introduce noise into a sensitive part of the cct. A rotary switch with valves above and below what is on the cct. would be a good way to go. Single pole, 4-way double gang should do it.

I found the amp was good with the NFB value stated but then i didn't experiment either. The amp was better with NFB though.

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