Those are cool observations and info points. Just wondering though about the 2019 thing. This current thread? Or some other thread in a link? I may be missing something….
Planning a 5F2a
- Thread starter ArcticWhite
- Start date
Going by the size of that choke, and that it looks like an HT choke, and that you know it came out of a Hammond, (and assuming there’s nothing wrong with it*) then yes, you (probably) can happily use it for a whole-of-supply choke in a CLC filter in a single-ended amp running a 6V6 and a preamp tube - because that sort of amp will only draw about 40-50mA tops, and what you’re holding looks like a 40-50mA choke. (No guarantees implied or given.)
* If the amp blows mains fuses when you first turn it on, it’s probably an indication that it won’t work.
* If the amp blows mains fuses when you first turn it on, it’s probably an indication that it won’t work.
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Humidity and corrosion can lead to the early death of transformers.
I highly recommend Blencowe's books. The guitar oriented book is intermediate level, but his hi-fi book starts with some relatively basic electronics info. You really need to get your head around alternating current, amplitude/period/frequency/phase (periodic functions), and impedance.
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Same circuit, but note that the power transformers listed on 5F2-A and 6G10 are different (66709 vs 125P1A). I believe there's a change in vendor in there (Triad to Schumacher? or vice-versa, or is that OTs?) but my suspicion is that a 6G10s B+ voltages were significantly higher (though within Fender's "20%" fudge factor).
To confuse matters, I have a photo of a 5F2 that's clearly got a Triad PT numbered 7787 (model or serial #?).
And here's a 1960-61 5F2-A that was for sale (for 2000 GBP! [the transformer in the cab corner is obviously a 125>220 converter]) with a slew of pictures, showing a PT with apparent model # OP-250B bearing also number 606036 (there is a better closeup photo of just the PT), which I thought might be a serial, except that I found post in a thread (search for either number if my link doesn't go directly to it) discussing a 1954-55 Champ with exactly the same numbers on the PT. According to the poster, that's a Schumacher. I actually think that the 6-digit number might be a date or date/serial code, since I've found a few references to "606" numbered 5F{1|2-A}s, with different last 3 digits. Note, interestingly, that the OT in the picture is a 125A2A, which is exactly what's listed on the 6G10 schematic @King Fan has posted above.
Nevertheless, I suspect that the PT used for Tweed Champ and Princeton was the same item (why change it for a tone stack?), and the 5F1 layout clearly has 340 V as the B+ at filter cap 1. That's what I'll be shooting for. BTW, the thread linked-to above has a reply, just below the one mentioning 606036, where the poster reverse-engineers the PT voltage:
"5F1 used a 275-0-275 I think. Here's how I came up with that...
According to the 5F1 layout Fender shows 340V at the first filter cap. Add 50V to that (the typical voltage drop from a 5Y3 rectifier at those low voltages and current draws)... 340V + 50V = 390V
"With a full-wave rectifier on a center-tapped transformer, divide that by 0.71 to get the un-rectified AC input voltage... 390V / 0.71 = 549.3V
"Since it's a center-tapped transformer, divide that by 2: 549V / 2 = 274.5V
"So, a 275-0-275 transformer for a 5F1 is what you are after to stay true to the original."
There is some good info here like the size of the filter caps but the info wasn’t correct. As shown the maximum capacitance is 32uF.
Also you don’t want your rail voltage to exceed 360VDC or you will need a different cathode resistor on the 6V6.
The big question is how are you going to use the amp?
If you are going to drive the amp hard and loud I wouldn’t use a choke from the first B+ node to the screen grid B+ node, the voltage will be too high and you will destroy 6V6’s. In this case the 10K resistor is the better option.
Personally, I would prefer to use a sturdy choke before the B+ to the output transformer to filter out mains hum. There has been a post suggesting to use Pi filters with resistors instead of chokes. The problem here is sag, the amp for lack of a better term browns out and sounds muddy.
Then there is the guitar you will use with the amp, if you are going to use a Fender style guitar stick with Fender plate and cathode values, if you are going to use Gibson style pickups then consider Skylark plate and cathode resistor values. Both are good amps.
Good luck with your build.
Regards
Mark
Also you don’t want your rail voltage to exceed 360VDC or you will need a different cathode resistor on the 6V6.
The big question is how are you going to use the amp?
If you are going to drive the amp hard and loud I wouldn’t use a choke from the first B+ node to the screen grid B+ node, the voltage will be too high and you will destroy 6V6’s. In this case the 10K resistor is the better option.
Personally, I would prefer to use a sturdy choke before the B+ to the output transformer to filter out mains hum. There has been a post suggesting to use Pi filters with resistors instead of chokes. The problem here is sag, the amp for lack of a better term browns out and sounds muddy.
Then there is the guitar you will use with the amp, if you are going to use a Fender style guitar stick with Fender plate and cathode values, if you are going to use Gibson style pickups then consider Skylark plate and cathode resistor values. Both are good amps.
Good luck with your build.
Regards
Mark
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Brimar says potayto:
Others say potahto:
RCA Receiving Tube Manual 19??
GE 1955
Tung-sol 1959
RCA 1961
And finally, we have the real-life examples of people who load the 5Y3GT with twice the "typical operation" 20 uF and more, and there doesn't seem to be a literature supporting failures as a result of that.
Others say potahto:
RCA Receiving Tube Manual 19??
GE 1955
Tung-sol 1959
RCA 1961
And finally, we have the real-life examples of people who load the 5Y3GT with twice the "typical operation" 20 uF and more, and there doesn't seem to be a literature supporting failures as a result of that.
ArcticWhite
Tele-Afflicted
Attachments
Right; lots of good info in your post. Among those who've loaded the 5Y3GT with double the 20uF 'typical' capacitance is Fender; although the early schematic didn't show it, most VibroChamps and all Broncos were shipped with the first 2x20 in the cap can jumper'd together to make 40uF. These amps have never been noted to eat 5Y3s. The 10-20 uF "typical" and 20-32uF "max" values we hear (and see in data sheets) are said to be a throwback to the early years; when RCA introduced the 5Y3 in 1935, caps bigger than 10uF were rare -- and expensive. For that matter, note Leo ran 2x16 to get 32 in the 5F2a even as late as the '50s.
Here's my '67 VibroChamp...
Here's the Bronco...
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ArcticWhite
Tele-Afflicted
There Choke is used after the first filter capacitor and the voltage drop comes mostly of the coil resistance and less of a Choke charging the current and releasing the current. That change the filter operation to CLC. I think choke gets mostly "wasted" as voltage regulating component but still does filter the Mains Hum. Obviously this CL order is used because sag-effect is considered good and it comes when regulating is not good.
Sometimes of even more often on push pull instrument amps the Choke is used after B+1/OT input but before B+2/Screens supply (together with Screen dropper resistors) and purpose there seems to be prevent stages interact with each other.
ArcticWhite
Tele-Afflicted
A couple more progress shots. All the hardware is in, but I need more room for the big caps, so I'm going to move the fuse to the opposite face, next to the power switch.
Planning to use metal film resistors in the signal path. Can anyone tell me where I should use carbon comp instead?
BTW, the choke is in the middle. I'm going to start with the little OT that came with the amp, and probably sub in a larger one later for comparison.
ArcticWhite
Tele-Afflicted
OP here.
I built the amp as a P2P, but attempted to follow current best practices grounding schemes, so there's a lot of ground wire running all over the place. It's kind of a mess to look at.
It worked pretty great for about thirty minutes, and then started making loud click/pop noises when I hit A string notes, hard at 70% volume.
Chopsticked it and reflowed everything, tried different 8ohm speakers, and swapped a bunch of tubes with no change.
Then the OT gave it up with a puff of smoke. It still works, but now there's a lot of noise, so I'm assuming the OT is partially fried.
I used the smaller of the two OTs from the original stereo SE amp because it didn't have the center tap that the other one has. I assumed it was compatible with an 8ohm speaker but looking at this schematic it's very hard to tell.
Anyone want to take a guess at what impedance the center tapped OT would like to see? I've included a closer view, but the text is pretty illegible.
I built the amp as a P2P, but attempted to follow current best practices grounding schemes, so there's a lot of ground wire running all over the place. It's kind of a mess to look at.
It worked pretty great for about thirty minutes, and then started making loud click/pop noises when I hit A string notes, hard at 70% volume.
Chopsticked it and reflowed everything, tried different 8ohm speakers, and swapped a bunch of tubes with no change.
Then the OT gave it up with a puff of smoke. It still works, but now there's a lot of noise, so I'm assuming the OT is partially fried.
I used the smaller of the two OTs from the original stereo SE amp because it didn't have the center tap that the other one has. I assumed it was compatible with an 8ohm speaker but looking at this schematic it's very hard to tell.
Anyone want to take a guess at what impedance the center tapped OT would like to see? I've included a closer view, but the text is pretty illegible.
