Here's an odd power amp. This was used to amplify a set of chimes with pickups on each chime tube for outdoor speakers. 50 Watt output with several impedance taps using 4 6L6''s in parallel push pull. When I installed the organ back in about 1980, I had to hook this system up to the organ. I believe I may have replaced a couple of tubes at that time. The chimes have long since been replaced as the original were cracking. So this amp has not been in use for at least 25 years. I was at the church today to service the organ and for a slight reduction in the bill, they gave me the amp. I have no idea what I'll do with it or if I'll even rebuild it. I called Paul Rowe of Maas-Rowe today to see if he had a mate hiding in the parts archives. If I could find a mate, I could sell a stereo pair on Ebay to some audiophool. Unfortunately, Paul said they threw out most of the tube stuff years ago. He still had some replacement transformers, though! If they are output iron, I may buy them off from him. Interestingly, there is a 6E5 as an output indicator.
Once this amp is gone through and working well, I'm sure there are more than a few guitarists who might be interested in it. There is a resurgence of interest in tube amplifiers for musical work.
Hmmm. I thought the 5U4's were higher. But I've been wrong before!!! If I restore this thing, I'll bring it back to original. 5U4's are probably more common and the ones that are in there are "recent".
Well, I wouldn't bet on my knowledge of it either bud, . . .The 5U4 came in these jukeboxs I've tinkered with , and I compared them to the 5Y3s of Voice of Music amps I've had, . . . but it looks like the 5Z4 has still, the greater plate voltage capacity of either.
(This post was last modified: 10-02-2019, 10:13 PM by Jake Blake.)
In many cases the 5U4 can be substituted for the 5Z4. The 5U4 has a somewhat higher current capacity than the 5Z4. It seems in the case of your amplifier, that such a substitution was possible.
5U4 is a stronger tube, but if the 5Z4 is designed in, then it has to be examined if the filament winding has the capacity for the additional 1A of current.
The opposite is OK, if the current capabilities of the 5U4 are not called for.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
The amp uses 2 rectifier tubes, so the total difference if you use 5U4's instead of 5Z4's will be 2 full amps draw on the power transformer. This might overheat it some. I would go back to what it calls for, the 5Z4's.
Good point on the heater current. The schematic also lists a 5V4 which has a slightly higher capacity, still 2 amps heater current. The 5V4 and the 5Z4 are cathode rectifiers rather than filament. Don't know if that makes much difference other than slightly slower in supplying current to the filter sections which is 32mfd at 600v (2 x 16mfd in parallel).
I don't have the exact schematic of this amp. Paul Rowe of Maas Rowe is looking to see if he has one. However, it is very similar to this 500A schematic except that the 4 6L6's were replaced by 2 6550's. Can someone splain to me function of the 6V6 in the screen grid circuit of the 6550's? I would assume it is some form of regulator for the 6550's (6L6's). Perhaps protection for excessive output?
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