Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Wanabejimi on September 28, 2020, 04:16:53 pm
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I’ve built a Princeton Reverb with 5881/ 6l6’s. I used a Deluxe Reverb PT and a 45 watt OT. It has two mods. First, it has a switchable tonestack….from Blackface Fender Treble/Bass to Tweed with just a single tone knob. The only other mod is some tweaks to the trem do get the 5881’s to wobble more than they were. I’m curious about the volume of others who have built 6l6 PR’s? This amp is not as loud as my Deluxe Reverb. The Deluxe R at just under “3” is the same volume as the PR on “5” (maybe even a little louder). My 5e3 deluxe is also louder. I recognize that the PR has the combination of a cathodyne PI and the Fender BF tonetack. There is a pretty decent jump in volume when I switch to the tweed tone control. I should also note that the amp sounds great and sounds just like a PR should.
All the voltages check out. I’ve got 441 on the plates, 425 on the screens, -40 bias voltage with a bias of 38ma
Thanks!
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The Deluxe PT doesn't have enough mA current to drive 6L6s properly, IMO
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A schematic with voltages would be helpful.
It’s a matter of voltage gain and power handling. The size of the transformers matter, as does the configuration of gain stages
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Maybe use a Super Reverb PT.
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That doesn’t seem right.
Is 38ma The current per 6L6? Did you install an adjustable bias pot? If not I’d start there and push your current a tad higher. To me there is no way it couldn’t be louder than a standard deluxe. You have the tube power and the current capabilities to be way louder.
I just built a modified mojotone Princeton kit. I did a Hammond 270ax (only 100ma) and an Allen TO20 (20 watt OT). Woth 6v6’s, it goes toe to toe with my buddy’s handwired Deluxe.
If that’s not enough I’d also encourage you to check out the stokes mod. I tried it a few days post-build and noticed a big jump in headroom. My PI plate voltage is now around 260v, instead of 200-210v. I like it a lot. That’s part of the reason it competes with the deluxe.
Are you comparing volume through same speaker, or could speaker efficiency be a factor?
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There is a pretty decent jump in volume when I switch to the tweed tone control.
of course there is. the tweed TS has about 1/2 loss than the TB/TMB types.
The Deluxe R at just under “3” is the same volume as the PR on “5”
both amps have a different preamp gain structure and power output levels. ex., one could build a preamp amp/power amp combination that would be unplayable at "3" or "5". the deluxe reverb has 1 more gain stage (the LTPI) than the princeton reverb does; that is likely why.
--pete
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I’ve built a Princeton Reverb with 5881/ 6l6’s. I used a Deluxe Reverb PT and a 45 watt OT...I’ve got 441 on the plates, 425 on the screens, -40 bias voltage with a bias of 38ma...
If the OT primary impedance is around the typical 4k level, my guess is that a DR type PT will be rather overstressed at high power outputs, and due to the high idling current, it won't have chance to cool down.
Can you hold your hand on it after it's been idling a while? Does it get too hot to touch with a fingertip more than momentarily after it's been cranking out high power for a while?
Bear in mind that Iac is around 10-30% higher than Idc, and a DR PT's HT winding may only be rated for less than 140mA ac.
The point being not to be surprised if the PT fails.
...-40 bias voltage with a bias of 38ma...
Regarding terminology, just to note that the -40V measurement here (ie between the control grid pin5 and the cathode pin8) is the bias; with a tube it's always a voltage. Whereas the 38mA measurement will probably be the plate or cathode current at idle, ie no signal applied to the control grid. This condition may also be referred to as static or quiescent.
The bias voltage controls the plate current at idle, this being a key aspect of a stage's operating point.
I acknowledge that the terminology tends to be widely misused, I just trying to clarify things for you.
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Thanks!!! Thank you to everyone who replied. I'm going to get a bigger PT. I really appreciate it!