Re: Problems with custom amp...
- From: Mr. Crag <mc@xxxxxxxx>
- Date: Sat, 24 Sep 2005 00:04:50 -0700
Never buy custum. Buy a name brand like Crate, AMpeg etc.
On Wed, 20 Aug 2003 13:42:19 GMT, "Jack A. Zucker"
<jaz@xxxxxxxxxxxxxx> wrote:
>I bought this thing from a small amp builder. I thought it was a good deal.
>Let me just say that folks were right and that you get what you pay for.
>
>Anyway, it's basically a 50 watt Fender Reverb, single channel style amp.
>375-0-375 PT, GZ34 rectifier, 2 6L6, (2) AX7 and (2) AT7 tubes, big BF
>Bassman size output transformer, no choke, yada-yada. Slight variations upon
>the AB763 circuit, minus the vibrato.
>
>This thing has been a nightmare from the beginning. Speaker that didn't fit,
>power tranny center-tap not connected, ground side of screen supply filter
>cap not connected, cold solder joints, non shielded wires going to the dwell
>control (causing squealing), power tranny getting EXTREMELY hot, power
>supply and screen grid caps rated at 450V though they are seeing 475V,
>yada-yada.
>
>I've got everything fixed (including changing all audio components to AB763
>values). The outstanding issues are the power transformer overheating and
>the underrated filter supply caps. I have a quad of 350V 100uf caps on order
>to run in a totem-pole arrangement (original value was 47uf) but I'm not
>sure how I'll fit them in because they are currently on the board and
>there's not room for 4, side by side or 2 stacked (it's a 2" high chassis
>and the board is .75" up from the bottom. One idea is to cut holes in the
>board and stack the caps using cable ties and RTV to hold them together.
>There's no room under the chassi unless I want to mount the 4 caps on the
>opposite underside of the chassis from the power tranny.
>
>Another option would be to play it close to the hilt and try to find 47uf
>500V caps or somehow try to fit an LCR 50uf/50uf 500V can inside the
>chassis. Not sure I want to drill a huge hole in the chassis and even if I
>do, I'd have to put it on the opposite side due to space considerations...
>
>The other possibly larger problem is the power transformer. It's made by
>handwound transformers.com. I've heard many nightmares about them. It's a
>375-0-375 tranny and it's rated for 6A on the heater tap and 3A on the
>rectifier tap. Even at practice volumes and a fan blowing on the tubes and
>the transformer, it get so hot that the chassis is almost too hot to touch.
>The fan keeps the tubes very cool so I know know it's the transformer
>itself.
>
> I tried putting in a weber copper cap to see if not drawing down the
>rectifier heater would make a difference. Since this transformer is a tad
>too hot for my use, I think I may look into getting a decent quality
>350-0-350 transformer. Something like the Hammond 273X (120VA, sec.
>350-0-350, DC ma 110, Fil.#1(rct) 5.0v @ 2a, Fil.#2(htr) 6.3v @ 4.0a ct)
>
>If I wanted to ditch the rectifier tube and go with a full wave bridge
>rectifier (w/no centertap), In that case since I wouldn't be using the
>rectifier tube I'd probably go with a 330-330 of 340-340 transformer. anyone
>have any recommendations? Yes, I know I should use google. I will
>
>P.S.
>
>I don't want to go off on a tangent but this one is the 2nd amp I got from
>him. The first one had even more problems. I could have returned this amp
>but I would have been charged shipping 4 ways (for 2 amps) including fedex
>overnight to get the first one back so we worked out a deal where he sent me
>a $200 rebate and I agreed to fix the amp myself...
>
>P.P.S.
>
>I hope this is enough information. I don't want to get accused of trolling
>again... :-)
>
.
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