Tube Amps / Music Electronics
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|12/26/2005 2:41 PM|
||Re: SF DeluxeReverb:4ohms cab?|
I've heard warnings for years, but haven't actually seen a power transformer that went down while using 6L6's. I don't even recall the people giving warnings actually experiencing failure while using 6L6's. Replacement power transformers don't list the A's available on the 6.3v taps.
Same thing as the parasitic oscillation caps. Although I know it's possible to have an oscillation problem after removing the suppression caps, I've yet to see the amp that goes into oscillation.
I always tell someone blackfacing a SF amp to monitor the temp of the output transformer after removing the caps to make sure it ain't happening. (Oscillations may not be audible.)
In theory, the oscillations should show up in at least a percentage of these amps.
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|1/3/2006 9:38 AM|
"I've heard warnings for years, but haven't actually seen a power transformer that went down while using 6L6's. I don't even recall the people giving warnings actually experiencing failure while using 6L6's."
Steve, I put RCA NOS 6L6GCs into my 64 Deluxe (no reverb) and the PT died by the 5th gig. The heater voltage was reading 6.2 vac after the tubes were installed. Could have been it's time to go but strongly recommend using either an additional heater xfmr, or replace the rectifier w/diodes. Also pulling the tremolo and NORMAL channel 12AX7s will provide a slight heater current advantage. IMO BobW
|1/3/2006 12:28 PM|
Now I can honestly say, I heard of my first case. Checking the heater voltage drop should indicate whether the current draw is too great. Replacing the tube rectifier won't lessen the heater draw as the rectifier uses a separate heater winding (5 volt supply for the rectifier tube VS 6.3 volts for the other tubes.) But it will allow the transformer to run a slight bit cooler if the 5 volt rectifier supply isn't used.
I actually got my DR as a power transformer repair. I replaced the power transformer and retubed it in the early 80s, and when the customer disappeared never picking the amp up, I ended up with it.
I've got a great sounding set of RCA 6L6's that draw twice as much as any other tubes I've used. A couple amps I've had them in didn't have enough range in the bias to bring them into line. (I realize that has nothing to do with the heater draw.)
|1/4/2006 9:08 AM|
Steve, Could be apples vs oranges. Those tubes draw more heater current than the 6L6GCs, etc., so I imagine your replacement PT is probably heftier than the original Fender. What manuf/model are you using? and is the Plate voltage the same/higher? My 64 was replaced with a Magic Parts PT and the B+ was 15V higher. In order to keep the amp at the same approx break up volume, the power zener trick was used to reduce it back to original specs. I suspect, but can't say for sure if the original PT died due to the 6L6GCs but now I no longer have an original PT
Transformer designers will sometimes install thermocouples into new proto designs to accurately measure core/winding temperature. Not practical for mass production. BobW
|1/4/2006 10:14 PM|
After talking with Paul at Mercury Magnetics I will repeat what I was told about deluxe tranny's. They had so many different one's it's mind boggling. If you look at the schematic it says 325v on the deluxe and 330v on the BFDR. Also I was told early BF deluxes had smaller OT's than the BFDR's. So it's a crap shoot and most will probably hold up, but then you might have a weak one for whatever reason and it goes down.
I also noticed the BFDR has 2 10K resistors on the B+ rail and the deluxe has a 10k then a 27K. Must be a reason, I haven't opened enough of them to know and I do not know why. I can guess (reverb, extra tubes and such) but I am not sure. I only owned about 5 or so dr's and 1 bf deluxe non verb which sounded better than all the DR's I had.
I was told from a guy in Nashville about 5 years ago a lot of guys are upgrading their deluxes after blowing out their PT's from running 6L6's, some chop their chassis for bigger iron. I think that's why MM makes the bigger stacked more iron version of the BFDR tranny. I'm guessing and it's just hearsay, but it makes sense.
|1/5/2006 10:52 AM|
It was a long time ago...over 20 years, but I got the replacement from Fender, and it was the transformer used in the last silverfaces, so the voltages were higher as it was meant for a 5U4GB rectifier.
A shorted cap took out that transformer in the late 80's. There were other burned parts, but my memory is fuzzy. It's a dead issue now (no pun intended). At that time I decided to use whatever I had on hand and not put any more money into it. I used a transformer, larger but it fit with an adapter I made. The voltages were too high for current production 6V6's then, so I use 6L6's and cathode bias which gets it back into 6V6 tonal territory of lower gain, and some compression. It's been too good to change it further. I've done some other changes but none are non-reversable. I'll let whoever ends up with it when I'm dead have the fun of restoring it to stock.
I stopped drilling holes in blackface amps long ago after the mod-police broke my fingers.
In the 80's they weren't prized at all...especially the early 80's. One store in Wisconsin had Bandmasters and Bassmans stacked like cordwood for $75-125 depending on the condition.
I will admit that most of my experience with Deluxe Reverbs other than mine is mostly silverface. I see them less and less as the years go by.
|1/5/2006 1:38 PM|
thanks Steve, I'll bet the cathode biasing sounds really cool in your DR.
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