Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Thisismyname on June 16, 2025, 11:11:45 am
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I have a DR clone that, long story short, no longer has the 2nd channel, or any if the effects.
It's essentially the stock 2 triode preamp, phase inverter, 2 6v6s, and GZ34 rectifier. It's using DR iron.
I'd like to convert to 6L6s. I have an appropriate output transformer. I'll thinking I'll work off of a Vibrolux schematic unless recommended otherwise.
My question; since my DR isn't using the triodes for the normal channel, "vibrato" and the reverb, my power transformer should easily be able to handle the current draw, right?
Anything else I should look out for in this conversion?
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The current draw on the heater winding stacks up, but on the HT winding 2 x 6L6s will need around 2 x as much current as a pair of 6V6s. Will this be okay? Time will tell.
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The 6.3Vac winding should be rated for 3 amps. As Tubeswell has mentioned. What Power transformer do you have? Brand model ?
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The 6.3Vac winding should be rated for 3 amps. As Tubeswell has mentioned. What Power transformer do you have? Brand model ?
It's a Mercury Magnetics FDR-PRI power tranny. It's their version of standard DR power tranny that is compatible with DRRI mounting holes. The spec sheet doesn't mention maximum ratings.
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One thing I forgot to mention is that I don't plan on wiring up the normal channel and effects when using the Vibrolux as a reference. It'll just remain a single channel bare-bones amp, just with 6L6s. I'll be using a 2 triode preamp. I'd be referencing the Vibrolux schematic for the power supply more than anything.
All this assuming it's safe to do so.
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Thing is if you look at PTs for amps running the 6L6 family they are all appear to be rated at 200ma and higher on the HV winding. The DR PTs are around 150ma. I saw that Mercury has a fat stack that might be rated higher than a conventional DR PT. Your dropping 3 small bottles - one is the 12AT7 reverb driver so I guess you might be ok.
Maybe send Mercury a message and ask what that PT's HV winding and 6.3v windings are rated. Or try it out and monitor the PT heat.
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A good practice for any electrical project is to create what is called a "power budget".
Identify the current draw (on each tap) of what you plan to build, then compare that to the published specs of potential power transformers. A basic handwritten table or a small digital spreadsheet will suffice for a tube amp.
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You are going to to need larger transformers, use Vibrolux 6G11 parts and machine chassis to accept.
--Pete
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12AX7 draw 0.3A at 6.3V, so losing 3 of them balances out the additional 0.9A of heater current that the 6L6 draw.
The issue is from swapping the OT to a 4k type. Its 1k class B loadline allows a fair chunk more HT current draw than the 1k65 class B loadline of the standard Deluxe 6k6 OT.
I suggest to make an 'in use' evaluation of the amp with the standard 6k6 OT, then with the Vibrolux OT.
If the Vibrolux wins out, then in the long term you'll need a beefier mains transformer. In the short medium term, you'll probably get away with it, provided you don't crank the amp / idle the 6L6 up at 21W.
In my Vibrolux based build, I prefer a DR OT :dontknow: