Picking up where I left off, the tone switch bank - which is on another harness, needed all wires replaced. Each one was desoldered, and used to pull a new length of wire through the shielding braid. Most of these wires terminate at a board with capacitors mounted on it... and I didn't have all the values, so wires were tacked on until I can do the caps one-by one. This is a very cramped area of the radio, and it made for slow work.
On the audio power amp/PSU, I got the 50 mfd + 50 mfd cap restuffed and the end crimped over. That chassis is almost finished, aside from a couple of caps that, again, I was missing the correct values.
Good progress... And progress on other projects for the HiFi...
Lots of other things got in the way this weekend, but I did get a few minutes work on the Zenith. Audio amp/PSU is now completed, with the last replacements of rubber wire and caps, I suppose it could be hooked up and tested as-is.
Next, recap of the radio chassis, but I'm waiting for an order of parts to come in.
It is slow-going, but the recap work is progressing. This chassis is quite deep, and access is difficult in a few places where components are snugged in around valve sockets. some areas have screening/shielding panels as well, making it tighter still. Anyhow, I got all the tone circuit, audio section and back towards the detector and discriminator circuits done. I think it is a little over half-way, with the most cramped area now completed.
Now, I'm wondering how I'll align the set, as I do not have the "Wave Magnet" loop antenna to hand - it is in the cabinet, 300 miles away. One option is to bring it back next trip. The other is to finish up here, and take the alignment gear with me. Perhaps this will spur on the work
Another search for info - actually I was looking for operating instructions for the sake of interest - turned up the Nostalgia Air files for this radio. Lots more info, including the simplified schematics which help understand what is in play for the different band selections. I'm really pleased to have this, similar info for my RCA was very helpful in finding out the capacitors which were upsetting oscillator tracking on the SW bands.
Funny how things don't look tricky until you start work. I got all but one of the paper caps changed on the RF chassis today, but it was more fiddly than expected. That last cap shouldn't be a problem, but I ran out of time.
At one point, working around an IF transformer, I was concerned about internal connections.... One of the paper caps was fitted so that the lead passed through two terminals on the transformer. One of these terminals had no continuity. This prompted me to the lengthy detour of removing the transformer, and opening it up. Of course, that leg showed that it had never had a connection in the first place. Back it all went.
Thinking now about simulating the "Wave Magnet". From the schematic, it is clear that it has a center tap, grounded, such that the feed to the receiver is balanced. I also need to configure an output transformer and speaker for audio testing.
the audio output transformer can be had in a few varieties,, there will be an 1, 2, 3, C and a metallic ground tab mounting terminal.
one of the letter terminals will "sound" the best on the speaker you have or the speaker you have chosen ,, but its all about impedance matching.
they are not overly expensive.
i got mine from antique electronics supply pn P-T291 for 17$, its 8watts.
this may not be what you pick, but just saying there are options
(This post was last modified: 02-03-2019, 01:54 PM by jcassity.)
Actually I have one already (Bought in case I needed it for my Philco) - and was just looking it over on the bench. I need to configure it for 8k impedance (or the nearest tapping) plate-to-plate for the 6V6 output valves, and find a safe way to wire up the HT.
The original speaker and OPT are safely in the cabinet 300 miles North, but took up too much room in a very cramped car, so just the 3 chassis made it here for phase 1 of the work. 3 chassis? Oh yes. The radio deck, Powe amp and PSU, and a little chassis for the Zenith phono preamp. Still have to recap that one, but it is not needed to run the first round of tests.
The chassis passed the first "dim bulb" test with the valves removed. Moving on now through the test steps after a spot of lunch. More later
She passed all the dim-bulb trials, and there was a feint scratching from the speaker with the bulb still in the line, and the rectifier connected, when the volume was rotated. At this point, only about 70 V HT was available instead of the 300+ one should get with a direct connection to the mains. So I removed the bulb tester...
Switch on.... wait... very quiet, but then a bit louder scratching... nothing more... then a whisper of static rose to audibility. We're switched to the 100 MHz FM band. Twiddle the dial. Voices, music!
She lives!
Rather distorted audio on FM, but signs of life on all bands, indicating that the oscillators all work, and the RF stages. Next stop to figure out the alignment procedure and see what improvement can be achieved.
Always a good day when a project glows back to life
on your slug tuning for the FM part........something i had happend to me.....
on my zenith, its fm is slug tuned but since i did not know what i didnt know,, i did a modification.
the metal plate atop the tuning cap seemed to be "not following" my tuning properly,, it was sorta delaying in dropping down the slugs into the coils. i zip tied a weight to the metal plate i called an "elevator",,, cause i am not an expert..
then... i noticed on some other slug tuned FM sets there is a spring that pulls the elevator back down.
on your set i notice your chassis sits at an angle,, so..... make doubly sure that the elevator is following the tuning dial without any delays or hang ups.
i found a spring,, cut it to length and installed on my set to always keep some degree of reasonable tension on the elevator "with the slugs all the way *DOWN*".
not sure if this applies to you or not but pay attention to how your slugs follow the tuning knob.
Also,, on your tuning cap when you align the FM,, like i did, you will notice that you can jump forward to jump forward to just the two adjustments on the tuning cap especially if your already really close or split the difference on the AM vs FM dial needle location.
one mica cap moves your station either left or right of what you have the needle on and the other cap increases or decreases the audibility.
find a station on fM from a modern radio then find it on your tube radio...
observe where your needle is pointing...
if your really close then you can simply adjust FM station as needed the two mica caps on your tuning cap.
if your way the heck off........ well..... then you align.
(This post was last modified: 02-04-2019, 11:59 AM by jcassity.)
I remember your tuning problems - and checked this chassis at the time you posted . On my chassis the follower is workig well.
Lots of adjustments yesterday, and it is working much better. I still have to complete the tracking and antenna trim for FM. Alas, also, I had a frozen "slug" in the discriminator transformer which cracked on me. Although I could make adjustments, and have things much better, I found a scrapper chassis online which will provide the appropriate donations.
Even with a small test speaker sat on the bench, this radio seems to have nice sound, no hum and good clarity.
The patient survived the transplant, and is alive and well.
Before doing any desoldering, I tested the adjustment of the cores in the donor discriminator transformer. These freed up with only a modest twist of a plastic trimming tool - that was a good start. Then, on to desoldering and carefully untying the wiring to the transformer in the restoration. This was very time consuming, as I wanted to preserve component leads for an easier job with replacement. It seems I do need a better pair of needle nosed pliers for this sort of work. With that done, it was deja-vu all over again, as the donor part was removed from the junk chassis. It was cleaned up, and installed into the good chassis without too much trouble, save for re-twisting the component leads carefully.
Soldering complete, it was on to alignment. Again, I found adjusting the discriminator to be confusing. It calls for peaking up a dc measurement while adjusting the primary, and zeroing the dc offset while adjusting the secondary. Well, whatever I do, I can't get a sensible reading on the first measurement when using the recommended IF signal injection (8.3 MHz). Perhaps not enough injection signal, but the audio output certainly indicates that it is making it through. Following this method resulted in a pretty deaf radio with distorted audio. The discriminator was clearly well out of kilter.
So instead, I peaked up the IF stages, and adjusted the discriminator on to a station. A peak in volume followed primary coil adjustment, and clarity followed secondary adjustment. Result: nice clean tuning, stations across the dial, and clean audio
Next, I have to rig up something to tune up the Medium and Short Wave reception (standard 455 kHz IF procedures) but FM came first, as that is likely the primary demand from this radio.
I had a royal case of frozen slugs in my Zenith 8G005 TO.
Cracked three. One more had to go in during alignment and refused to go back.
Most feeed on their own and/or with the help of a tool I made out of a nylon rod and fiber glass tip made out of old PCB.
Though aligned, I eventually bught a donor chassis and used some coils from it. Surprisingly, all th coils from it didn't have the problem.
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.
Missing the "Wave Magnet" loop antenna until the electronics return to the cabinet, I hadn't really tested medium wave performance.
A wire attached to the antenna terminal resulted in statons with awful hum. 60Hz pickup was overwhelming the RF stage. Then I remembered I have a ferrite rod in the parts box. This was connected as would be the wave magnet. Lots of stations, and performance peaked up using the old trick of moving the coil on the rod to get the proper inductance. AM sound quality on this set is excellent!
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