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In Reply to: RE: My amp plan posted by Kindablue on October 28, 2015 at 06:14:08
What boards are you putting in?
I believe the original board used a 7199. Most of the replacement boards use a 12AU7 - a fine tube. And the board should be replaced. The 7199's are not available and second Dynaco NEVER meant for those boards to be around this long. But there is an adaptor for the 7199 to a 6GH8.
There really isn't much to do on those amps. Pretty good just as they are. But yes the driver board should be upgraded.
I also think that amp uses 0.1uf coupling caps. Invest in a good set of PIO caps. It makes a difference. Some people say to change the resistors. Me - I like the sound of those carbon comps. But if you do have to change any use metal film. They sound good and still maintain a degree of vintage sound. Metal film resistors are great - no question. But have a VERY clean clear sound. NOOOOO vintage sound there!
If you're really ambitious replace the sockets. A source of trouble in the future.
Post you results.
charles
Follow Ups:
When I said use metal film WOW - was that wrong!!!!
I meant use carbon film. Funny story, but Radioshacks resistors are really quite good. I have NO idea what line or brand but they are excellent resistors - sonically speaking. These are the 1/2 watt carbon film in either multipacks or separate packs.
Even on the drop in replacement boards, see what resistors are in the signal path. A lot of upgrade boards typically replace the carbon film with metal film. Still a wonderful sounding resistor - but a very clean sounding resistor. Great for SS sound but not a vintage sound.
charles
6gh8a seem to sound okay in a Dynaco with an adapter or wiring change if one can't find a 7199. The Japanese ones sounded really good to me.I think that Radioshack resistors are the same as Xicon's sold by Mouser. My local Radioshacks are all closed:(. Over the years they sure came in handy when I needed to fix something quick.
On the resistor front, some metal films like Vishay-Dale CMF/RN65's sound great in vintage amps. Jim McShane has send me a lot of em when he's helped with rebuild kits.
Edits: 10/31/15
In spite of bleats to the contrary, 1 size does NOT fit all. "Horses for courses."
Metal film resistors are excellent in grid to ground positions, as they are inherently low noise.
Carbon composition resistors make good grid stoppers, as they are both non-metallic and non-inductive. Yes, carbon comp. parts can be noisy. However, the noise is function of current and current in a grid stopper is negligible.
IMO/IME, you select parts based on the specific role to be performed. That which works well in 1 situation may be G_D awful bad in another.
Eli D.
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