Car Tube Amp

[Craig D]

Hi all. This is my first post. I'm also quite new to tube amps but really like what I hear. I am busy building myself a tube amp for my car. As i'm quite inexperienced I've taken advise from a friend to follow the simple circuit diagram of the Dynaco ST-70. All is going well and I have all the parts including the chassis. Where I am feeling a bit concerned is in the preamp/phase splitter tube. The original circuit requests a 7199 that is totally unavailable in my part of the world. With a slight mod I could use the 6U8. When I google the 6U8 I seem to find very negative opinions on it. Could someone advise me on whether this tube is in fact ok or if there is another tube or even 2 tubes (one for the preamp and one for the phase stlitting) that I could use instead. If so possible diagram on connecting up would be appreciated. Thanks. Craig.

[w5jag]

In the ham radio world, a lot of people complain of short tube life in 6U8, mostly from grid to cathode shorts. I've never had a 6U8 go bad, and I have a lot of them in service in various radios.

6EA8 and 6GH8 are common replacements. I have no idea how any of them would work / sound in audio service.

Win W5JAG

[rcavictim]

6AN8 works very well in the similar circuit of the Dynaco Mk-II with P-P UL 6CA7`s.

For the vibration in a car amp I think I`d be looking at more robust output tubes like 6146 or 829B. Float the output tubes on a subchassis plate on rubber isolator suspension.

If you want to be really classy get a vintage dynamotor in the trunk to provide the B+ supply.

[ray_moth]

I wouldn't call a 6146 particularly robust. 807 would be a better bet, IMHO.

The CEO`s and Managment are all idiots and by wasting precious time, are helping seal our doom!

That sounds like a good description of what killed off British Leyland.

[7N7]

Originally posted by ray_moth
I wouldn't call a 6146 particularly robust. 807 would be a better bet, IMHO.



That sounds like a good description of what killed off British Leyland.

British Leyland was killed before birth, by first, the stupid incompetent Labour government that conceived the idea (it should never have existed) and second, by that ****** Stokes who ran it. End of story.

7N7

* I am not allowed by this forum to type the word w****r. I hope that you know what w****r means to English eyes.

[rcavictim]

Originally posted by ray_moth
I wouldn't call a 6146 particularly robust. 807 would be a better bet, IMHO.



That sounds like a good description of what killed off British Leyland.

The 6146 got banged about in many mobile radiotelephones and taxi radios on the 2 meter band (where one tube could make 30 watts RMS FM carrier) and seemed to survive it. A 2E26 was used to drive it in one ancient Motorola radio I am familiar with and once owned.

[Colt45]

Yeah, 6146 is plenty tough for mobile use, that's what it was designed for.


People give it a bad rep for them starting on fire with screen voltage over ratings.. use it within spec and it's robust as hell.

[Hotsauce]

Loctal base tubes would give you a fighting chance against vibration.

7N7 is identical to 6sn7 except for pinouts. Cheap and easily available most places.

John C.

[Eli Duttman]

Craig,

I don't enjoy raining on somebody else's parade. However, an important point that has only been hinted at has to be made.

How do you propose to convert the "12" VDC in the car's electrical system into the "450" VDC needed by EL34s?

For the pentode/triode in the Dyna circuit, use the 7059. The 7059 is a "12" V. heater version of the 6U8 intended specifically for automotive service.

[7N7]

Originally posted by Eli Duttman
Craig,

I don't enjoy raining on somebody else's parade. However, an important point that has only been hinted at has to be made.

How do you propose to convert the "12" VDC in the car's electrical system into the "450" VDC needed by EL34s?

For the pentode/triode in the Dyna circuit, use the 7059. The 7059 is a "12" V. heater version of the 6U8 intended specifically for automotive service.

Easy: just buy a SS inverter and build a normal valve amplifier.

7N7