Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: bruno on November 16, 2010, 07:04:06 pm
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Did you notice any difference to a regular 6l6 model? Will the el84 hold the high plate voltage supplied by the tremolux transformers?
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Never heard one, but I saw one at an studio auction once.
I bet they eat 6BQ5s fast. If I had to build or service one, I'd be sure to add 1.5K grid stoppers and 1K screen resistors.
http://www.el34world.com/charts/Schematics/files/fender/TREMOLUX_6G9.pdf
I think those 30-35 watt Fenders with 6L6s sound great--Tremolux, Vibrolux, Pro, etc. So I'd probably build one of those rather than an EL84 Tremolux.
Ken
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Here's an excellent source of tube data sheets:
http://www.mif.pg.gda.pl/homepages/frank/vs.html
That Blonde Tremolux has 400 volts on the 6L6 plates. The Design Center maximum values for 6BQ5s is 300 volts on the plates and the screen grids. I bet it would eat power tubes fast!
There are several Brown/Blonde Tremolux schematics in Doug's Library which show 6BQ5 power tubes. However, the grid return resistors, grid stoppers (or lack thereof), and screen grid resistor values are appropriate for 6L6s, not EL-84s. Take a look at the Marshall 18-Watt for one known-good EL-84 circuit:
http://www.el34world.com/charts/Schematics/files/marshall/marshall_18watt_schem.pdf
I'm certain that you would be better off with a PT and OT tailored for the different power tubes. Based on the tube data sheets, an 8K primary on the OT looks reasonable for a pair of EL-84s with 300 volts on the plates (subject to a more knowledgeable person's correction). A pair of 6L6s with 400 volts on the plates OTOH wants to see somewhere between 3.8K and 5.6K (Fender used 4K IIRC).
A single channel version of the Blonde Tremolux with EL-84s and the right voltages/iron could be a very fun amp.
Oh, I didn't look at the tremolo circuits, but you don't need nearly as high a signal to jiggle EL84s as you need to jiggle 6L6s. There's an old thread in the Archives you should find for adjustments to the bias-vary tremolo for different signal levels (and range of speed).
Hope that helps,
Chip
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Well I'd assume he meant a quad of El84s not a pair, so the 4k OT would be just about right. As for the high voltage, lots of EL84 amps run the voltage that high, it's the current he needs to worry more about. For instance the AC30 runs the tubes at design max. but eats tubes because the dissipation is so high.
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A quad of EL-84s would like the 4K OT primary, but what's the point? I'd rather have two 6L6s personally. Besides, the schematic for the 6BQ5 version of the Tremolux only shows 2 output tubes.
Chip
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What about using an OT with an 8K primary for a pair of 6V6? I ask because I am using an OT like this on a 5e4 biuld and need to know if I should like add some resistance in there or...???
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8K is perfect in a Fendery amp using 6V6GTs with cathode bias and OK in fixed bias.
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Phweeeeeew!!! wipes the seat from his brow. I chose a Out put Tranny for a Marshall JTM 45 for this biuld almost a year ago when I was planning on making this chassis into an 18 watt Marshall Clone. Mainly because I just really don't like thewimpy open bell iron that usually finds its way into the low watt amps nowadays.
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That amp is one of the rarest of Fenders.
I think they only built it for about four months.
I never heard one, that I know of, but I'd guess you'd get
a combination of EL 84 chimeiness with Brownface Fender
warmth and tube trem.
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I have a friend that has one. It's sweet! He builds his own amps and that's the only factory amp he won't part with.
Dave