Tube Amps / Music Electronics
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|9/3/1999 3:15 AM|
||A few more homebrew pics...|
For anyone who's interested - I took a few more pics of the chassis removed from the amp last night. They're up on my web site
|9/3/1999 4:49 AM|
Here's a suggestion Nick,
440vdc sucks big time for any 6V6GT!!
These amps sound pretty good with a pair of 6L6GCs at.
But it looks like you have the standard reissue aftermarket silver face TMI power supply trannie in there and it was wound for a 5U4 rectifier tubes not a 5AR4.
So, use a 5U4 instead and also install an 18v 5W zener diode in the high voltage supply center tap to ground.
Go over to your bias supply circuit and use what ever resistor you need to (the grounded one) and restore the negative bias voltage back so as to get about -45vdc at max.
|9/6/1999 12:56 AM|
I really need to take some better measurements - the supply voltage seems to be all over the place - in the past 2 weeks I've measured it anywhere between 236 and 263V! Anyway - I'm going to a) get myself some new tubes and b) take the variac home and do some proper controlled measurements.
I hadn't considered the possibility that the power transformer was not wound for a 5AR4. It's actually a Mojo model 26V6P - is this the same tranny you're talking about? I have the data on it at home - what should the
ratings be for a 5AR4? (ie no load voltage on the HV winding and 5V heater current rating?).
|9/6/1999 5:52 PM|
I don't know for sure but it looks like a Pacific or a TMI tranny.
I'll take a look at the ones I have when I get back to the shop and compare.
MOJO has used a few different transoformer manufactures over the years and it depends on how old the PT is as to who made it.
I heard they are now they are using the same as what Fender is using.
Since there are only a small handfull of good cheap companies out there, it can only be one of them.
You should see the EIA code stamped on one of the bell ends if it was an aftermarket winder like:
Pacific...1052, TMI... maybe it's a Schumacher...606, etc etc.. I know New Sensor has quit using Thodarson and have gone to an production agreement with Schumacher! YEAH!
Right off the top of my head, I can't think of any of them that wound a PT for the BF DR/5AR4,they all seemed to have chosen the silver face model for some reason.
Those are all about 110ma and with a 5AR4 you can figure the medium loaded B+ to be well over 425vdc.
The 5vac filament is 3a.
I've used a ton of them in higher idle current 6V6s and medium idle current PP 5881 type amps.
The can get very hot when drawing lots of current but they are pretty darn good when used in spec.
|9/6/1999 6:07 PM|
||Re: A few more homebrew pics... Revisited|
Yes I went over and look at the chassis again and I'm sure it's a PT for a silver face Deluxe Reverb (the lamination stack is about .375" thicker in the siver face amps) and the only way I've been able to use those in a black face Deluxe with a pair of 6V6GTs is with a 5U4 rectifier and or installing a series of 5 watt zener diodes in the B+.
That same transformers in this amp work really well with a 5AR4 or solid state plug and a pair of 5881s biased about 15-16 watts at idle though.
It will give you a different tone and power output option.
Even the "smallish" Deluxe OT seems to be able to handle the larger 5881 tubes fine.
|9/3/1999 1:27 PM|
|tubegirl||Re: A few more homebrew pics...|
|9/3/1999 5:37 PM|
..That really is looker! Nice work. For your trem "ticking", just drop a .01uF cap on the left side of the "raoch" (as you face the back of the chassis) Just shunts the HF hash from the neon to ground. (there was a Fender memo on this once upon a time)
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