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> New project: Bogen head to 5e3
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SeniorBean
Junior tube assistant
Posts: 1
(4/16/04 1:49 pm)
New project: Bogen head to 5e3
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I am not a technician, but a hobbyist. I am about to take on my biggest project, but I have some things I can not seem to find the answers on.
In the past I have done tone tweeks, cap replacements, trans replacements, and even did a Hoffman PTP board in a Bassman RI way back when Doug was making them himself.
Okay enough excuses-
I bought a Bogen HF10 amp (It has inputs for tuner, aux, and mag on the back) at a flea market for $30. It was cheap, in great condition, looked really cool, and had the magic combo of 2-6v6, 1 12ax7, and 1 12at7, and a tube rectifier. It currently is all original inside (PTP, not even terminal strips) and it may have the original tubes. The caps are shot. I am guessing its of 1950's mfg. After trying for some time to find the schematic, and unsuccessful, it looks like its a prime candidate for a Hoffman 5e3 board. It does not have a circuit that is recognizable as being close to a known vintage guitar amp.
The output transformer needs to be replaced. The power trans made need to be replaced depending on the answers I get.
The Rub: the rectifier is a 6x5gt, and I have not been able to find any info on it used in guitar amps. Its an octal socket, it takes 6.3 volts, and draws only .6 amps on the filament. Our common rectifiers are 5 volts and 2-3 amp on draw. This tells me I can't sub, say a 5y3 without blowing the trans.
I'll be honest about me skills- Even if I had all the "stats" on the recto, all of the other projects I have done have been "remove this, replace with that."
My question (finally): Can I use the existing power transformer, and 6x5gt, and install a 5e3 board?
Or should I just start from scratch, and treat this as project chassis, and gut it entirely?
Or should I be repairing it to original spec? I don't have much use for a vintage 10 watt PA amp, and it does not seem to have a collectible value.
Thanks. Be kind to the newbie.
Tiny Daddy
I will work on all amps
Posts: 612
(4/16/04 2:18 pm)
Re: New project: Bogen head to 5e3
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Just a few notes to get you started: I would guess 1960's manufacture. You can use the original power transformer but 6X5 is really wimpy so replace with 1N4007 diodes. How much voltage is the power transformer putting out with no load? You may need higher-voltage power supply caps than what's in there. Also be careful with the AC wiring and bring it up to modern times with a 3-wire line cord.
SeniorBean
Junior tube assistant
Posts: 2
(4/16/04 2:44 pm)
Re: New project: Bogen head to 5e3
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I read 540 volts at the rectifier at pins 3 and 5. 270 from pin to ground.
Thanks for the advice on the cord.
Tiny Daddy
I will work on all amps
Posts: 613
(4/16/04 3:24 pm)
Re: New project: Bogen head to 5e3
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OK so 1.4 X 270 = 378V so use 450V filter caps. Other than that, just pick a schematic from SchematicHeaven.com with a similar number of tubes and make some modifications.
SeniorBean
Junior tube assistant
Posts: 3
(4/16/04 3:51 pm)
Re: New project: Bogen head to 5e3
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That 378 volts would be the plate voltage, correct? 6v6's max plate voltage is 315 volts. Right now, this amp reads 268 volts on the plate. Wouldn't using a ss rectifier cook the tubes pretty quick?
ganzonimx
Hey get your own solder
Posts: 464
(4/16/04 3:56 pm)
Re: New project: Bogen head to 5e3
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You could use a Weber Copper Cap instead of the rectifier, that would give you the sag of a rectifier and you would not use any heater current...
Do you plan to install the new board inside the same chassis? I converted a Radson record player with the same tube set up to a 5e3. First I intended to install everything inside the original chassis but ended up with intractable hum 'caus of long wires I ended up installing everything into a new chassis/cabinet - now everything is cool...
Chris
bnwitt
Senior tube assistant
Posts: 332
(4/16/04 3:56 pm)
Re: New project: Bogen head to 5e3
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Bean,
don't take those data sheet max plate voltages too seriously. The blackface deluxe reverb amp runs 415V on the 6V6GT plates. On my 5E3 amps I normally run anywhere from 365V to 380V at the plates. Tiny's right on. Also, as stated, the webervst equivalent 5E3 copper cap rectifier would save you heater current, but I think with the diodes your voltage is purt near perfect for a Tweed deluxe. Chris' other point regarding lead dress causing hum is a good one. When you are designing your circuit board(even if you need to make it longer then necessary)you should try to have the wiring points line up with the tube sockets as much as possible to keep the wires from the board to the socket pins as short as possible.
Edited by: bnwitt at: 4/16/04 4:03 pm
SeniorBean
Junior tube assistant
Posts: 4
(4/16/04 4:28 pm)
Re: New project: Bogen head to 5e3
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Thank for the tip on the Copper Cap. Is solves my main challenges, including adding a standby switch. The fact that it looks trick helps (all the tubes are visible on this chassis).
When talking about the "voltage drop", I'm assuming that's in comparison to a ss rectifier.
As far as lead length, it a pretty small chassis. Its about the same size a 5e3.
bnwitt
Senior tube assistant
Posts: 333
(4/16/04 4:54 pm)
Re: New project: Bogen head to 5e3
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You are assuming correctly. With your ouput voltage of 270-0-270 on the PT, you might want to get the copper cap with no voltage drop that Weber makes, that is if you are after the 5E3 tone. On the other hand, all you really have to do is mount the diodes on the proper rectifier tube socket pins and you have made your own copper cap without sag anyway. The only down side to that is you can't easily change back to a tube rectifier easily. The copper caps don't cost that much either. Regarding not adding a standby switch, that is really if you are going to use a tube rectifier that takes a while to warm up and put high voltage on the tubes. With diodes, a standby switch is a good idea so the tubes can warm up before you pop em with voltage. A copper cap with sag will still come to voltage very fast as opposed to a tube rectifier.
Edited by: bnwitt at: 4/16/04 4:56 pm
Tiny Daddy
I will work on all amps
Posts: 614
(4/16/04 7:38 pm)
Re: New project: Bogen head to 5e3
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You will not get 378 volts of plate voltage because the voltage will drop to a lower value when a load is connected. Also the output transformer primary will drop some voltage. And if the amp is cathode-bias, subtract another 12 Volts or so. But the filter caps may see 378V momentarily until the tubes warm up.
bnwitt
Senior tube assistant
Posts: 334
(4/16/04 8:32 pm)
Re: New project: Bogen head to 5e3
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Tiny,
I expect the additional voltage drops as well and this is why I think the solid state or no voltage drop copper cap is his best bet for a 5E3 B+ range. I'm using 350-0-350 PT's with 5Y3's and getting 365Volts on the B+ rail under load. Starting with 270-0-270 is low for that set up. It would probably be a good clean amp but not what one wants for guitar, more like the PA that it was. What do you think?
zachsdad
Posts: 12
(4/17/04 6:07 am)
New project: Bogen head to 5e3
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Remember, the fun is experimenting and learning. That way when the project is finished and sounding great (your opinion, not someone elses) you know why. Not because someone else said to put part A in Slot B. Be careful and enjoy. For most of us its still just a hobby.
Leslie
bnwitt
Senior tube assistant
Posts: 335
(4/17/04 9:39 am)
Re: New project: Bogen head to 5e3
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I agree with zachsdad to a degree. Opinion's fine for simple tone variance changes in a circuit, but math is essential when trying to get a stable tube circuit and more so when trying to emulate a particular circuit like the Tweed Deluxe. You need to start with some basic values in the voltage range.
bluesbear
Hey get your own solder
Posts: 360
(4/17/04 9:45 am)
Re: New project: Bogen head to 5e3
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I don't know about the HF10 but I have 2 CHB20's, 2-6V6 20 watters. Same deal as yours, 6V rectifier. One of mine has the 2 part speaker cabinet that encloses the amp with the 2 12" speakers. Just for fun, I decided to see how it sounds before I messed with it so I got a screw in adaptor and plugged a guitar in. T-Bone Walker reincarnated! This thing sounds like the best of 1950. It's a one trick pony but it does that trick better than any other amp I've ever heard. It's gotta need electrolytics by now but I'm afraid to touch anything, at least until there's an
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