I was on the yahoo list for a brief moment in time as "centralheating1978@ yahoo.com".
Glad to finally be on this list since tube amps are a big interest for me.
I bought a big 1957 wurlitzer 4420 organ for sixty dollars. The amplifier in the back is a tube amp, with all the original RCA tubes in there.
I would like to know if I am able to replace a tube without fucking something up? The tubes are obviously very old, so the amp probably has gotten used to running things differently. If i were to put a new tube in there would it be a problem to the other components ?
Heres the tube list,
-7025
-12AX7
-12AU7A (3 of 'em)
-7027A (2 of them)
-5U4GB
(8 tubes total)
Heres some photos too
Best
1957 tube amp. Original tubes!
Moderators: pompeiisneaks, Colossal
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70sSoundQuality
- Posts: 12
- Joined: Wed Jan 19, 2005 12:34 am
- Location: CA
1957 tube amp. Original tubes!
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Last edited by 70sSoundQuality on Sun Nov 19, 2006 10:47 pm, edited 1 time in total.
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70sSoundQuality
- Posts: 12
- Joined: Wed Jan 19, 2005 12:34 am
- Location: CA
Re: 1957 tube amp. Original tubes!
heres the organ that came with it;
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Re: 1957 tube amp. Original tubes!
Hey John!
I'm glad you appreciate the seriousness of working around HV circuits, and remember if you're not sure what you're doing it's always smart to take it to a qualified tech to have it looked at. I know you weren't impressed by your local tech when it came to your Super, but, depending on where you live, someone here might be able to give you the name of someone who does solid work. Replacing the filter caps (those silver metal tubes, and perhaps there might be one or two inside the amp) will certainly be more technically challenging than pulling the chassis, and it will require a few tools to do the job, so again if you're not comfortable it's worth it to bring in a professional. I'd hazard to guess that those caps might say "Mallory FP" on them, right? Can you read the values on them, in Volts and Farads (it'll be in uF, like 8uF)? Replacing the power cord is a little bit easier, but it still involves poking around inside the chassis, soldering, and working with a strain relief.
The heat you mention is an interesting point. Is it all the tubes that just feel hotter to you, or is it just the 7027As? This can be a problem, but isn't necessarily so. What you'd want to look for is any orange or red areas starting to form on the biggest internal parts of the 7027s (the "plates"), flat dark metal pieces that surrounds most of what's inside. If these are turning color, turn off your amp, as it will need to be rebiased. Part of what's probably causing the extra heat is that in 1957 (actually, I think the 4420 came out in 1960 or '61) the wall AC voltage was lower than it is today (by about 10 volts ac). Plugged in nowadays, those tube filaments see more voltage and will get hotter as a result, though I'm not sure if it's all that noticeable. As far as the Super was concerned, you *should* definitely be able to feel heat on your power tubes or something's not right; they should actually be pretty uncomfortable to touch after they're fully warmed up.
It's really a shame, but Baldwin actually had a schematic for a 4420 on the net, and that could really come in handy later on, but when Gibson bought them out it seems to have disappeared. Oh, and I meant to add, are there any codes written on the speaker that you can see?
Matt
I'm glad you appreciate the seriousness of working around HV circuits, and remember if you're not sure what you're doing it's always smart to take it to a qualified tech to have it looked at. I know you weren't impressed by your local tech when it came to your Super, but, depending on where you live, someone here might be able to give you the name of someone who does solid work. Replacing the filter caps (those silver metal tubes, and perhaps there might be one or two inside the amp) will certainly be more technically challenging than pulling the chassis, and it will require a few tools to do the job, so again if you're not comfortable it's worth it to bring in a professional. I'd hazard to guess that those caps might say "Mallory FP" on them, right? Can you read the values on them, in Volts and Farads (it'll be in uF, like 8uF)? Replacing the power cord is a little bit easier, but it still involves poking around inside the chassis, soldering, and working with a strain relief.
The heat you mention is an interesting point. Is it all the tubes that just feel hotter to you, or is it just the 7027As? This can be a problem, but isn't necessarily so. What you'd want to look for is any orange or red areas starting to form on the biggest internal parts of the 7027s (the "plates"), flat dark metal pieces that surrounds most of what's inside. If these are turning color, turn off your amp, as it will need to be rebiased. Part of what's probably causing the extra heat is that in 1957 (actually, I think the 4420 came out in 1960 or '61) the wall AC voltage was lower than it is today (by about 10 volts ac). Plugged in nowadays, those tube filaments see more voltage and will get hotter as a result, though I'm not sure if it's all that noticeable. As far as the Super was concerned, you *should* definitely be able to feel heat on your power tubes or something's not right; they should actually be pretty uncomfortable to touch after they're fully warmed up.
It's really a shame, but Baldwin actually had a schematic for a 4420 on the net, and that could really come in handy later on, but when Gibson bought them out it seems to have disappeared. Oh, and I meant to add, are there any codes written on the speaker that you can see?
Matt
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70sSoundQuality
- Posts: 12
- Joined: Wed Jan 19, 2005 12:34 am
- Location: CA
Re: 1957 tube amp. Original tubes!
I finally got the balls to plug my bass into the tube amp. The trouble is that the tube amp is connected to the organ, both at the power switch and to the speakers. In any event, the first thing I noticed was that my bass was LOUD but CLEAR at the same time! This thing really sparkled for my string instrument, much more than the organ reed itself. The only problem is that there was a fuzzy/distorted sound in the background. It was as if I was playing clean and fuzzy at the same time.
I then took the tube amp RCA jack (out) and plugged it into my VCR, which is connected to a small television that has two 3 inch speakers. They sound much smaller, but much clearer than the organ's speakers. Not to mention that fuzzy distorted sound was not present on the TV speakers. I'm conviced the old Jensen voice coil shit the bed in the organ speakers.
The amp really sounded clear, I was extrememly excited. The bass tone was "round" and full, and really excited in the upper midrange area. Doing bass palm mutes and picking away at the "munsters" theme song really sounded authentic with this amp.
1) On the amp chassis, there are two main inputs, one called treble, and one bass. The bass one works fine, but the treble one seems to not process any signal, just a really high pitched squeal.
I then took the tube amp RCA jack (out) and plugged it into my VCR, which is connected to a small television that has two 3 inch speakers. They sound much smaller, but much clearer than the organ's speakers. Not to mention that fuzzy distorted sound was not present on the TV speakers. I'm conviced the old Jensen voice coil shit the bed in the organ speakers.
The amp really sounded clear, I was extrememly excited. The bass tone was "round" and full, and really excited in the upper midrange area. Doing bass palm mutes and picking away at the "munsters" theme song really sounded authentic with this amp.
1) On the amp chassis, there are two main inputs, one called treble, and one bass. The bass one works fine, but the treble one seems to not process any signal, just a really high pitched squeal.