Dynaco PAT4/Aikido tube preamp

[mr2racer58]

Hey All,

I have an old Dynaco PAT 4 preamp gathering dust. I just recently finished rebuilding my Mark VI's and they sound great! (To be honest the only Mark VI parts left are the transformers, chassis and the meters.)

But my question is this, could I buy one of the modern preamp kits, like the Aikido and use the Dynaco chassis and controls to build a nice tube preamp?

From what I've seen I would need a power supply, line stage and phono preamp stage. I'm curoious if this is possible? Or just a stupid idea?

Kevin

[Eli Duttman]

Not at all stupid. I have a PAT5 chassis that's been rebuilt by AVA into a hybrid full function preamp and it's just fine.

Dyna's mechanical engineering is good, but the controls are junk. Also, you need to nibble the back panel partially away and install a piece of FR4 PCB material to provide a footing for good RCA jacks spaced for modern interconnects.

You might make a go of the OEM source selector switch, but (IMO) you will be better off installing the economical Lorlin CK1459, for which Mouser (stock # 105-14572) charges less than 5 bucks.

In short, you have good sheet metal, hardware, and room to work.

BTW, refer to the attached Max Robinson designed circuitry for tone controls. It's possible to use ZVN0545A source followers instead of the cathode followers and hold the bottle count down, but anything simpler will wreck the sound. Even then, making the TCs totally defeatable is (IMO) correct.

[Looneytunes]

Hi Eli,

Is there any chance that you might have a slightly bigger copy of that schematic? There are a few values I can't make out.

It's must be my monitor.

Thanks,
Looney

[llwhtt]

mr2racer58,

If you don't mind me asking what did you do to your MKVIs? I have two early '90s Yakov Aronov amps which are basically two MKVI amps on one chassis, yes they are heavy. I know the xfmrs are mucho better than the circuitry that surrounds them. I have not been able to find any mods for the MKVIs.

Craig

[ChrisA]

Originally Posted by Looneytunes

Hi Eli,

Is there any chance that you might have a slightly bigger copy of that schematic? There are a few values I can't make out.

It's must be my monitor.

Thanks,
Looney

The schematic is near the bottom of this page. I was just reading it the other day
http://www.angelfire.com/electronic/...mp-Tone-A.html

[Gardner]

Hi Mate

I would suggest you to buy modern preamp kits and use the Dynaco chassis and controls.The parts would be fitted into that.

[cnpope]

Originally Posted by ChrisA

The schematic is near the bottom of this page. I was just reading it the other day
http://www.angelfire.com/electronic/...mp-Tone-A.html

Unless I'm missing something, this particular schematic doesn't seem to appear on the webpage you mention. I'd also be interested to see more about it, ideally with a higher-resolution file.
Chris

[PH104]

try here....

Audio Asylum Thread Printer

[mr2racer58]

IIwhht,

I replaced the circuit board with a point to point driver section. It uses a long tail phase splitter front end. A negative temperature coefficient resistor replaces the time delay relay tube for a soft turn on. (When you do this you can't shut the amp off and immediately turn it on or you have a spike that blows fuses.) The 7199 triode/pentode gets replaced with a 12AT7 preamp tube and the phase splitter is now a 12AU7. The output tubes are now KT 88's. I think I still have a copy of the schematic for the modification I could fax it to you, or maybe attach it to a post tomorrow. I got the original modification from a Southern gentlemen named William Hardy at vintageamplifierrestoration.com in Hattiesburg Mississippi. I had to further modify it by adding individual caps and resistors on the ground side of the bias pots for each output tube. And the cathode resistors on the preamp and phase splitter are lower values than Bill specified to get the tubes to draw enough current. My amps had about 120 volts more than his on the B+ than his and we never did figure out why. If you contact Bill he might send you a schematic and parts list.

[Eli Duttman]

Those members who want a better version of Max Robinson's tone control circuitry, please send me a PM that includes your EMail address. I will send you the schematic in a more readable BMP format, which (unfortunately) is too big to upload as part of a post.