I'm building a Fender Champ 5F1 but only have a 290BBX Deluxe transformer on hand, which has a higher B+ than the typical 5F1 transformer. I know this will raise the plate voltage across the circuit, and I’m curious about the impact on the rectifier tube, especially since the 5F1 is Class A and runs the 6V6 at high continuous current.
Will the higher B+ voltage from the Deluxe transformer place excessive strain on the 5Y3GT rectifier, potentially shortening its lifespan or causing overheating due to continuous high current in Class A operation? I’m open to adding resistors after the rectifier to bring down the voltage for the rest of the circuit, but I’d like to understand if this would adequately protect the 5Y3GT. Any advice or experience with similar setups would be appreciated!
Will the higher B+ voltage from the Deluxe transformer place excessive strain on the 5Y3GT rectifier, potentially shortening its lifespan or causing overheating due to continuous high current in Class A operation? I’m open to adding resistors after the rectifier to bring down the voltage for the rest of the circuit, but I’d like to understand if this would adequately protect the 5Y3GT. Any advice or experience with similar setups would be appreciated!
Just make sure that the series plate resistance in the rectifier input is equal to or greater than 135Ω and the 5Y3 will be fine. The 5F1 uses a 16µf first filter capacitor after the 5Y3. The conduction angle should be fine. Your B+ voltage will be significantly higher than the traditional 5F1. The 6V6GT is only rated for a maximum of 315v on the plate. You will likely need a series dropping resistor in the B+ line to keep from blowing out your power tubes. The added series rectifier plate resistances will drop some voltage, but likely not enough to get the B+ below 315V plus cathode bias voltage. Prototyping is definitely called for.
If you're gonna use a power transformer with that much more output, it's no longer a 5F1 and you shouldn't try to make it one. Use a bigger power tube, a 6L6GC or EL34, and a bigger output transformer that can handle the extra watts, say a Hammond 125DSE. Go big.
If you need to drop volts, here's a way to do that: MOSFET Follies It's at the bottom of the page. This should give much better regulation than a series dropping resistor.
I considered doing this to fix an overvolt problem that turned out to be solvable by using a 5U4GB instead of SS power diodes. Turned out the junk box Stancor PTX was designed specifically for the 5U4GB to give 350VDC.
I considered doing this to fix an overvolt problem that turned out to be solvable by using a 5U4GB instead of SS power diodes. Turned out the junk box Stancor PTX was designed specifically for the 5U4GB to give 350VDC.
Your are absolutely right. That wouldn't be a 5F1. I'll buy the right transformers if necessary. I already built a Princeton Reverb so no need to go big. I'll keep it small. Thanks
Maybe mixing your advice with the MOSFET Follies proposed by Miles would lower the B+ to the voltage of the 5F1 (maybe the aa764) I just want a smaller amp that the Princeton Reverb I built. I don't understand "Just make sure that the series plate resistance in the rectifier input is equal to or greater than 135Ω " Do you mean to place a resistor before the rectifier tube?
Miles, that's very interesting and would read the Mosfet follies document and digest slowly. Thanks so much.
If you're thinking about a small amp, may I suggest you look at my Lil Champski design. A small 35VA power transformer can power one EL84, or a Soviet 6P1P, for a killer 3w amp, for about $200 in parts.
Maybe you don't like the comparison but it looks similar to the 5F1 with some mods isn't? Although the tube is not the same. Do you have any sound sample?
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Well that makes sense. I'm new to tubes and it puzzles me to use have of the transformer power for the rectifier.
I may give it a try.
Thanks
I may give it a try.
Thanks
So there's 2 ways to rectify the AC for use in the tubes - old way is a rectifier tube, new way is solid state. Rectifier tubes usually need a dedicated 5v winding, but the EZ81/6CA4 uses 6.3v and can be wired to the same source as the audio tubes. Rectifier tubes take
several seconds to warm up which means the HV comes up slowly, easier on the audio tubes. As a guitar player, you may prefer the added Sparkle that a rectifier tube can give. Solid state rectifier, either Full Wave or Bridge Rectifier, is cheap, instant and rock solid, but can impart a harsh edge to guitar amp distortion, so more cap filtering is necessary, IMHO.
several seconds to warm up which means the HV comes up slowly, easier on the audio tubes. As a guitar player, you may prefer the added Sparkle that a rectifier tube can give. Solid state rectifier, either Full Wave or Bridge Rectifier, is cheap, instant and rock solid, but can impart a harsh edge to guitar amp distortion, so more cap filtering is necessary, IMHO.
Yeah, that is what I was wondering: those two RC filtering can't be enough. I got the Hammond 269EX whith this specs:
Let's see what I can come up with. Should be fun!
Thanks for your help.
| VA. 43 |
| Primary 115 |
| 380V C.T. @ 71ma. |
| 6.3V @ 2.5A |
Let's see what I can come up with. Should be fun!
Thanks for your help.
RC filters are ok for a guitar amp. 5F1 being the prime example. 269ex would work if you use a SS rectifier. The real Champ uses 290AX 325-0-325@100mA gives a b+ around 360v. You can also try 270DX but I prefer the "Laydown" style transformer, it's shorter, you can make a thinner cabinet, put the amp chassis closer to the baffle.
That is for tube rectifier. I believe SS rectifier needs further filtering that the commonly found in small amps like the Champ.
That's true. This schematic
has a more elaborate filtering scheme for SS rectifiers. Same tube voltages as the 5F1.
e: or you could use a 68uF 450v cap as the reservoir cap and connect that to the OPT. Or a 100uF.
e: or you could use a 68uF 450v cap as the reservoir cap and connect that to the OPT. Or a 100uF.
The 5E1 had a choke. Leo Fender probably put it in there because he was copying a radio's power supply from his day job. It's not really necessary. Chokes have their place in Hifi, a guitar amp makes the tone. CRC power supply is plenty good.
Just remember that a big part of the characteristic sound of the champ is the overtones produced when it's pushed hard. The distortion changes the rectifier drop and the tube responds to that change. This is partly due to the sag of the 5Y3 rectifier and the high B+ voltage applied to the 6V6. If you go to a SS rectifier, the amp is not going to have the tonal qualities you are expecting of the champ.
In a guitar amplifier, a tight power supply with lots of filtering generally results in a boring and forgettable tone.
Moved to Instrument & Amps per forum policy - lots of help here for building guitar amplifiers.