Build Thread: Fender Black Face Princeton - 5E3 Deluxe Amp

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I know there is the odd person here that can read schematics so I thought I would post part of a thread I had going in another forum. I was designing an amp and in answering a poster's desire for an amp that can do both Blackface and 5E3 Deluxe sounds and I realized the concept would fit well in an amp that I built but wanted to rebuild. So here goes nothing.

OK did some more figurin'. The first, second and Phase Inverter stages of the BF amp and the 5E3 run of of 250V so no having to change the supply voltage between them.

The outputs and screen voltages do change as well as the bias voltage. If you were so inclined you could have some solid state diodes in series with the 5Y3 and in BF mode two switch poles shunt the current around the 5Y3 giving you a boost in voltage of 50-60V putting the amp in BF territory. The BF amp uses a 6.6k output transformer while the 5E3 uses a 8k. I would stick with the 8k. With the voltage on the output tubes higher you need more voltage on the grid so an additional cathode resistor in series with the normal cathode resistor is needed. One pole of a switch can be used to short this resistor out when in 5E3 mode. In BF mode the other contact can connect another bias cap, 470uF, to ground which stiffens up the bias and makes it more like fixed bias. Another pole is used to switch the NFB on for BF and off for 5E3. The additional voltage will increase the voltage on the preamp sections making them a little more clean. I am not including a schematic for this version, don't want to freak people out. Anybody capable of making the amp with the voltage boost could draw up a schematic from the description. Now moving on to the simpler version.

Well two versions. There are always options and compromises. The first is the power supply does not change so the BF version has the same power as the 5E3, not a big difference but it is there. In these two versions the stiffening capacitor on the outputs cathode is increased. The difference is the first schematic you need a four pole switch to change the preamp version from 5E3 to BF but in BF you still get a Tweed channel. So in both modes you can change the NFB and bias stiffness, might find it useful. Oops, two 220k resistors on the Tweed channel, the right one should be gone, by switch pole S1D.




The next version, one four pole switch. There is a catch, when changing to BF mode the other channel is disconnected. The negative feedback and bias capacitor gets switched at the same time as the input configuration. You could easily enough have the Tweed channel hooked up also in BF mode, rather than where it is now connect it to the second stage input. The thing to remember here is that it will interact with the BF channel.




So there you have it, I think I exhausted the realistic options. The layout and the schematics should be able to give an electronically competent person enough to put together an amp with the features/complexity they want. Not for the first time builder, you have to consider wire routing when going off the beaten path. I am going to try the second last schematic, I like what it has to offer the most and I have a chassis that can accommodate it.

[Dru Edwards]

We have a few people here who have built amps. I think Clint has a 5E3 he built, although I may have those numbers mixed up.

Sounds like an interesting project.

[muscmp]

very interesting. you've got that on the tele forum too?
yes, clintj has done different amps and i'm sure he'll like this setup.
i've built two 5e3 deluxe amps. 1st was with robrob's lead marshall channel and nfb circuit. the second was with a tube depot kit on a printed circuit board. now i'm getting ready to do a point to point 5e3 clone with no mods. this one will replace the modded one that will go into a head so i can pair it with different speakers. once i finish this 3rd one, i'll sell one and keep the other. i'm using weber 12a125a speakers and they sound great. here is a pic of my two.

very cool idea to combine them both. i may back up one day and do a tweed champ just to do it.

good luck with the build. i like the second version too.
play music!

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[Tone Gopher]

You seem to be making the preamp stages unnecessarily complex. You could parallel both channels by using a single input, a 1M splitter, then go into separate preamp volume controls. No need for all this switching.

Similarly, you could just not plug into the undesired input. An A/B switch box in the front of the amp could provide on-demand switching if you don’t want to combine the preamps.

And yes, this works. I’ve done it on a blackface Bassman.

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Originally Posted by Tone Gopher

You seem to be making the preamp stages unnecessarily complex. You could parallel both channels by using a single input, a 1M splitter, then go into separate preamp volume controls. No need for all this switching.

Similarly, you could just not plug into the undesired input. An A/B switch box in the front of the amp could provide on-demand switching if you don’t want to combine the preamps.

And yes, this works. I’ve done it on a blackface Bassman.

The reason for the switching is to get the backwards use of the volume controls that Fender did. The other position has a regular Princeton voltage divider volume along with the BF channel. So in a way three amps. It is not all that complex to do if you are good enough to follow the signal path. I was going to do this with a single ended amp but the request for a BF-5E3 amp reminded me of an amp I have built that I wanted to change.





So not too complicated, just the addition of the four pole switch.

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Originally Posted by muscmp

very interesting. you've got that on the tele forum too?

Yes I do. I used to spend more time there on the amp thing where I tried doing all kind of things seeing how to squeeze the most out of standard circuits. I was going to do a lightweight get up and go amp with a pair of 12V6's (6V6 with a 12V heater) that got pretty complicated but shy of channel switching. I reduced it down because I did not have enough space in the chassis.



So a Bassman but rather than a treble bleed cap on the volume control a Tweed tone control. Normal Bassman second stage, the tone stack has a three position switch, bypass the tone stack, center a typical Blackface curve, down the Marshall stack. Pre-PI master and eventually reverb.

The phase inverter biasing, output bias from fixed to cathode and a power supply sag resistor will be on its own switch. So with the tone stack out and the power section on the spongey setting knocking down the gain of the second stage something like a Tweed 5G9 Tremolux. So again, multiple flavors from the same amp. I did have a 2203 Marshall cascaded input, again not enough room. Decided it would be easy enough putting a pedal in front of it.

Using a laptop brick PS and a high voltage switching board the all up weight of the amp should be about 20lbs.



The only thing keeping me back from building these is I have some guitars I have been making and I am trying to get some of them finished. In case you don't get to the Build and Repair forum, currently drying in my kitchen.

[clintj]

I think I remember that discussion. My idle thought was use a BFDR chassis, with the Vibrato channel built as a Princeton Reverb. Build the Normal channel as a 12AY7 based, 5E3 preamp w/ 2 inputs and the V/V/T control set, and splice the channels at the driver stage prior to the cathodyne. Add a fixed/cathode bias switch, and you should have a reasonable facsimile of the two amps especially with the lower voltage drop of a 5AR4 rectifier to bump up voltage for the PR circuit.

Someone, either ClassicTone or Hammond, makes a dual output power tranny with 600 and 660V HT secondaries. Could switch those to alter voltage, too.

[printer2]

Lot of options when you have the chassis large enough to play with. I usually start off with a simpler idea and start adding features until building the amp is like building a ship in a bottle. And I tell myself I won't do that again, and then I go and do it again. I want to take a break from guitars and build a few amps instead.