• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

ReZenith SE 6BQ5

G

golana

analog
Like everyone else, I have too many projects I want to do. But, I'm not working
{1 month now:sigh:}, so with all this time. Heres my project SE Zenith, comes rctf'd w/5u4, and no driver. I found this, http://www.angelfire.com/vt/audio/se6bq5.html, You guys are usually pretty opionated, so I thought ya'll might like something better. I think I have most of whats needed, so if this looks good, should be able to get at it. Thanks amundo, Mike
 
Register to hide this ad
zenith001.jpg


zenith002.jpg
 
The schematic seems to imply that your output transformers have an Ultra-linear tap. I can not tell if the OPTs in the pic have 4 wires, or 5. If you have the UL taps, you gain some flexibility, as you can make an amp that can have both triode and UL mode. Fun stuff! This will make for a very low powered amplifier (pentode is roughly 5wpc, UL 4wpc, triode 3wpc), but it's all really about the speakers anyway, isn't it?
 
It's actually a hum-canceling tap - it was cheaper to add a tap to the output transformer than to add another stage of filtering to the power supply. The power supply DC goes in at the tap and splits between the output and other stages. The plate resistance of the output tube and the filter resistor on the opposite end are in the same ratio as the transformer windings. So voila - 60 or 120 Hz hum current cancels!
 
I don't know about his FB scheme. It's taken from the output secondary to the cathode of the driver tube, no? It's a pretty big loop compared with something like an RH84, but it might work.

I have issue with the 80uF cap as the first element after his 5Y3 rectifier. 40 would be the max I'd use.
 
Sorry to resurrect an old thread, but I have come into a pair of output transformers from this same chassis (Zenith 3D32, 95-1660 opts), and I would like to use them for a junkbox rh84 build. These each have seven wires coming out. Can these be used as conventional SE opt's, and if so, which (four of seven) wires do I use? Tom Bavis mentioned a hum-cancellation tap, does this account for three additional wires? Thanks!
 
Hmm... I have a similar chassis from an RCA console.

attachment.php


I traded off the original OPTs for a pair of Edcor 5K:8 SE UL OPTs for another project. I may use this chassis for a mini-console project for my granddaughter. Since it will be totally enclosed I will probably mount the OPTs off of the chassis if I go this route and use the space from that and the no longer needed can cap to mount preamp tubes.

I have been thinking along the lines of the RH84 but I may instead go the UL route. I will want to use readily available tubes so I was initially thinking 12AX7 or 12AU7. AX7 probably has too much gain though unless I end up using NFB and AU7 has a somewhat suspect reputation (though at low voltage swing may be just fine). Another possibility is 6N1P as I have a couple brand new ones on hand and they might be the perfect compromise. No problem with the extra heater current as the PT also provided heater power for the preamp and tuner in the original.

mike
 
Last edited:
jsax420 said:
Sorry to resurrect an old thread, but I have come into a pair of output transformers from this same chassis (Zenith 3D32, 95-1660 opts), and I would like to use them for a junkbox rh84 build. These each have seven wires coming out. Can these be used as conventional SE opt's, and if so, which (four of seven) wires do I use? Tom Bavis mentioned a hum-cancellation tap, does this account for three additional wires? Thanks!
Click to expand...

Are the numbers on both opts the same? Just checking. Zenith came up with some wierd s... stuff. I've got a different from yours zenith SE EL84 chassis and the left and right opts are different numbers with different colored wires out of them.

What are your wire colors? The red and blue will go to the EL84 tubes. I think the others you want to deal with are Yellow and Black. Yellows being to speaker +, black to speaker -. Your meter should show continuity between Red to Blue; and between Yellow to Black; but not other combinations. (I'm fairly color blind so caveat emptor or some such thing.)
 
Last edited:
I don't remember 2 extra wires, I can look later this weekend.

The hum wire is the bare copper, to grd.

I dig that RCA, super cool layout. Where can you add a driver?
 
The numbers are the same, also they are the same size... Wiring is pretty faded, so telling the colors apart are a little tricky, but I believe I've identified three pairs of wires that show continuity. One set uses the bare wire, so I will assume that pair is the hum tap. Getting closer, one wire left unaccounted for...They wouldn't have put a screen tap on console opt's, would they? Thanks for your ideas, in any case I think this will be a learning experience.
 
The RCA is rather interesting. It is powered with a SS voltage doubler. It is SE stereo with only the output tubes on the power amp chassis. The 12AX7 driver was on the tuner preamp chassis. Since I would be losing the can cap I could mount a socket their for the driver. Since OPTs will probably be off chassis I will have a fair amount of real estate available for drivers in that area too. I could even open up one of the ports where the OPT leads came through the top of the chassis. Another option that was suggested to me was having the OPTs on the chassis per the original design and putting the driver out the back of the chassis perpendicular to the output tubes.

Given that the unit will be entirely enclosed in a wooden cabinet including the speakers I am not sure how important it will be to ground any part of the OPTs.

mike
 
Squidward said:
I don't know about his FB scheme. It's taken from the output secondary to the cathode of the driver tube, no? It's a pretty big loop compared with something like an RH84, but it might work.

I have issue with the 80uF cap as the first element after his 5Y3 rectifier. 40 would be the max I'd use.
Click to expand...

I know this is an old thread, but if I found it so somebody else might also. I'm doing a rebuild / stand alone mod of of one of these Zenith 3D32 amps and agree. If using a 5Y3, reverse the 40 and 80 uf caps using 40 for the main first node B+ so as to not over load the rectifier. You can also further reduce voltage by using the now unused 2nd filament winding as a buck by seriesing (the right way) it with the 120 volt line winding. When I did this, it lowered filament voltage to 6.4 VAC. Perfect. Also further lowers B+ of course.
 
Last edited:
You must log in or register to reply here.
Back
Top Bottom