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zenith PP 6bq5 console amp

J

JGlenn

Active Member
I just picked up this amp and want to make it into a stand alone power amp. I did this last year with a magnavox 175. should it be pretty much the same deal with this amp or with it be a bit different? I had fun doing the maggie amp and wanted to do another one and check out the sound of the el84 so this seemed like a good candidate. There are two umbilical cords still attached to this and i'm not entirely sure where to start. I know what the inputs and speaker outputs are but im not sure what to do with the rest of it at this point. anyone build one of these yet ?
 
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6BQ5 tubes are awesome

Haven't attempted this with a Zenith but have recently done so with a Viking (Canadian) SE 6BQ5 and recently a Fisher E-49 which is 6BQ5 (EL84) PP also.

Your best bet for success is:
- find a schematic as that will answer nearly any questions which come up
- post here just as you have done :thmbsp:

Good luck with this, I sure love the sound of 6BQ5 tubes as you can tell...
 
These type amps often have umbilical cords. Sometimes the amp in the console is interconnected with the preamp/tuner (e.g. to supply it power) and to the record player; there could also be a remote interlock/switch that you would need to bypass if that's the case.
Is there a number on that chassis that might identify the model to help hunt down a schematic? Pics can help too.
EL84 amps usually sound great, so should be well worth the effort to restore.
 
I figured there was some kind of switch on the console itself in part of that wiring. the guy said it worked when it was in the console but the cabinet was trashed so for 40 bucks with all the original zenith tubes which I hear are pretty good tubes just rebranded I couldnt pass it up. theres a sticker on the chasis that says 7D31 and 010701 is stamped on top of it, not sure if thats any help. the tube lineup is 2 12ax7 s
4 6bq5 s and a 5u4g rectifier if that sheds any light to the amp model

thanks for the help I cant wait to get this thing running
 
What is it that you're stuck with? You say you know where the inputs are located, and you have the speaker outputs identified, so you just need to know how to turn it on? After you get it powered up, you're pretty much done except for restoration and rebuild.

If you can, pics of the bottom side of the amplifier would be most helpful.

Just saw the schematic. You want to put a jumper between pins 2 and 3 on the molex connector.
 
well I got it to turn on by jumping out the molex conector as cademan said. I have no sound out of my test speakers though. that seems kind of strange the way the two secondaries of the output trans are wired together, also theres a short black wire coming out of the trans with the terminal strip on it that doesnt look to have aplace to go, should that be grounded? I just have three wires coming off that trans for speakers, red white and black and the diagram shows some sort of grounding plug. Do I need these for something ? when I put a signal on the amp the output trannys start to sing if I turn it up so I guess thats a good sign right. Can I just do away with that funky wiring and come straight off east trans to my speakers ?
 
The Black wire in the center is the Neg- For both speakers. This is on the transformer with the terminals. The red is for the right speaker+ and the white is for the left speaker+.,, I think? the outside connectors are for 16 OHM speakers?? Its been awhile since I messed with one of these.
 
coman61 said:
The Black wire in the center is the Neg- For both speakers. The red is for the right speaker+ and the white is for the left speaker+.,, I think? the outside connectors are for 16 OHM speakers?? Its been awhile since I messed with one of these.
Click to expand...

That seems to jive with the schematic. Apparently in the console there would have been a shorting plug that shorted the white to the +ve of one set of speakers and the red to the +ve of the other set. So connecting White/black to one test speaker +/- and red/black to the other test speaker +/- as Coman says should do it.
 
alright I got it going now that black wire still baffles me though. In addition to the black common wire for the speakers there another black wire that comes out lower on the trans and it only about 3 inches long... aparently I dont need it anyway but still I would like to know where it would of gone. so the rebuild begins tomarrow night, I'll try to get some pics along the way. I already started to clean and polish the chasis a bit and I plan to build a nice wood base for it.
 
A picture would be helpful here. According to the the schematic in the link that Tinkerbelle posted there should be no black wire on those transformers except for the speaker common.
 
coman61 said:
A picture would be helpful here. According to the the schematic in the link that Tinkerbelle posted there should be no black wire on those transformers except for the speaker common.
Click to expand...

The only other black wire in the schematic is the one from the right channel transformer lower winding which goes to the gray along with the orange going to the yellow, for the gray-yellow speaker-out connections (16 ohm speaker option?). Maybe it's that black or perhaps the "black" is a dirty gray? It shows 1.4 ohms on the schematic, so if that black measures ~1.4 ohms to ground then maybe that is what it is. As Coman says a picture would help to clarify.
 
I restored one, though it's a 7B31 chassis with 12AU7s for the driver tubes.
 

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that came out nice, I want to build something similar for mine. did you do away with that funky terminal strip on the output trans or did your just not have that ?
 
I didn't have one. It was tough tracing where all the wires went even with a schematic because most of their color had bleach out and faded.
 
yea im having the same issues looking at this one. I think I may have taken out a cap I needed to leave in place, now its not working. there were two caps on a 7 pin terminal strip under the power xfmr I clipped off last night thinking they werent wired to anything anymore but I think I was wrong. I'm pretty sure I need the .01 but im not sure about the .1
 
JGlenn said:
yea im having the same issues looking at this one. I think I may have taken out a cap I needed to leave in place, now its not working. there were two caps on a 7 pin terminal strip under the power xfmr I clipped off last night thinking they werent wired to anything anymore but I think I was wrong. I'm pretty sure I need the .01 but im not sure about the .1
Click to expand...

On the schematic there's a 0.01uF AC line-to-ground filter cap; there's also a 0.1uF that looks to be across the phono changer switch...if those are the ones you are referring to.
 
yes those are the ones im refering to, I'm pretty sure I can do away with the one for the phono changer right ? I was listening to this last nite for a few mins on some test speakers and then decided to bring it out into the finished part of my basement to try it out on some real speakers. I hooked everything up and got a pretty loud hum so I pulled the plug to switch polarity and it sparked when I went to plug it back it and tripped the breaker. the fuse in the amp didnt blow so I'm alittle worried. I didnt try to power it up after that I decided it would be best to start recapping it but am I wasting my time now? did I kill it ?
 
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