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Magnavox 300071-1 power transformer 5V 4A dual 5U4GA questions

opnly bafld

opnly bafld

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Edited after Dswankey's helpful post.
I have a 6L6 tube amplifier with a Magnavox 300071-1 PT and it came to me (3rd or 4th owner) with a pair of 5U4GA tubes for the dual rectifiers. In doing some research I found a post on antiqueradios.com that claimed the 5V for this transformer is rated at 4 amps which would seem to be a problem with 2 tubes that have a 3 amp filament current draw.

My questions:
Is it okay to use this transformer with 2 - 5U4GA tubes?
I think the obvious answer is NO and I have no way to find out what the builder included with it originally.
Would a tube with a 2 amp filament draw be better?
Which tube?

Thanks for any help.
 
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I assume the 4A rating = bad to use 2 - 5U4GAs

5V4GA? (less voltage drop)
5Y3G? (more voltage drop)

I know more information would be good, but I don't have much to go on.
Would taking voltages at various points with the 5U4GAs in help?

After having it on playing music for a few hours I noticed the transformer was very hot, that started my search for possible causes and I found some threads here discussing modifications, but I'm still not sure what rectifier tubes to use with this scratch build.
 
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^ I just like to help where I can so I just did some Google searchs for you, as to your question that's above my knowledge.

Hold tight I'm sure the more knowledgeable will be along shortly to help you out with an answer
 
You already know that two 5U4 type tubes, with their 3 amp filament draw, are too much for this PT. To answer what type (and how many) rectifier(s) are needed means we need more information about this amplifier. Is it stereo (4 6L6 tube types)? Some pictures (top and underneath) will help immensely.
 
Since there are 2 tube sockets wired in parallel for the rectifiers, I think I need 2.
 

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opnly bafld said:
Since there are 2 tube sockets wired in parallel for the rectifiers, I think I need 2.
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That is not an assumption I am willing to make at this point. Let's not forget that there are a few stereo push pull amplifiers with a single 6AR4 rectifier. If there are numbers on the output transformers and a close up of how they are wired we can get a good guess on the expected draw on the rectifier.
 
I have seen plenty of medium power push/pull amplifiers with just one rectifier, but this one was built with two and I'm not planning on redesigning it.

If it comes to that I have someone I can send it to and he can change things as he sees fit.
 
A pair of 5v4 would do fine I think. Good for 350ma steady state and 4 amps between them. Slow start, and not as expensive as 5ar4 in old production.

Pair of 5ar4 are good for 500ma and 4 amps of current draw.

Single 5u4gb is 275ma and needs 3 amps
 
ramjet said:
That is not an assumption I am willing to make at this point. Let's not forget that there are a few stereo push pull amplifiers with a single 5AR4 rectifier.
Click to expand...

I was able to contact someone that has some knowledge of the builder's designs, he suggested trying it with just one rectifier, it works.
He also recommended using two 5Y3s and 6V6 or 6P3S tubes for less power but an easy load for the whole circuit.
 
So far with just one 5U4GA the PT is running about 25 degrees cooler.

In a few months I think I will try some 6P3S tubes with 5Y3 rectifiers.
 
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6v6 and 6l6 tubes work into a fairly different load. ballpark of 10k vs typically in the 6.5k range. They also won't bias the same so if this was set up for a 6L6, I don't expect it would behave itself nicely with 6V6 tubes.

I don't suppose this is one of @GordonW's Magnavox builds? I know he used parts out of some PPP 6v6 mono Magnavox amps and converted them to PP 6L6 stereo amps.
 
gadget73 said:
6v6 and 6l6 tubes work into a fairly different load. ballpark of 10k vs typically in the 6.5k range. They also won't bias the same so if this was set up for a 6L6, I don't expect it would behave itself nicely with 6V6 tubes.
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I don' know if it was optimised for a specific tube. It was advertised as a 6L6 amp when I bought it from the second owner and the original owner also called it a 6L6 amp. They both listed other tubes that could be used.

I know there are 2 camps on this, build it for a specific tube or build it somewhere in the middle and offer a choice of tubes to make the customer happy. Either way, you hook it up and sounds come out.

gadget73 said:
I don't suppose this is one of GordonW's Magnavox builds? I know he used parts out of some PPP 6v6 mono Magnavox amps and converted them to PP 6L6 stereo amps.
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No, JWN. I was able to find the original owner's ad, but his information was limited and he does't remember many details.
 
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ah, metal fingerprint removers. Learned that lesson by accidentally bumping a metal 6F6. Talk about a nasty little oven of a tube, yikes.

I'll have to remember that one though. Looks like it wants a little more impedance per plate and has less peak current but should sub for a 5U4G in a fair number of places. Probably cheap too, people don't like those metal tubes. I've gotten a number of them over the years for peanuts compared to their glass-bottled siblings.
 
gadget73 said:
ah, metal fingerprint removers. Learned that lesson by accidentally bumping a metal 6F6. Talk about a nasty little oven of a tube, yikes.

I'll have to remember that one though. Looks like it wants a little more impedance per plate and has less peak current but should sub for a 5U4G in a fair number of places. Probably cheap too, people don't like those metal tubes. I've gotten a number of them over the years for peanuts compared to their glass-bottled siblings.
Click to expand...

Metal tubes might even be better but I don't like them for the simple reason the filament glow isn't visible. Real tubes glow, part of the charm, mystery of their operation. Real tubes glow and have their internals enclosed in glass, felt this way since my first look inside a radio, long time ago. Beyond mere glass are the sexy tubes with the mysterious metal cap with the wire attached that disappears though a hole in the chassis. As a kid, just fascinating, still has that charm.
 
spicer said:
Metal tubes might even be better but I don't like them for the simple reason the filament glow isn't visible. Real tubes glow, part of the charm, mystery of their operation. Real tubes glow and have their internals enclosed in glass, felt this way since my first look inside a radio, long time ago. Beyond mere glass are the sexy tubes with the mysterious metal cap with the wire attached that disappears though a hole in the chassis. As a kid, just fascinating, still has that charm.
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I also appreciate the notification of red-plating, which I would have anxiety about with metal power tubes. Small signal tubes and rectifiers not as much.
 
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