Back after a long hiatus... Admiral Tuner Help Needed - Page 2 - Videokarma.org TV - Video

UberVacTuber · #16 01-04-2015, 09:50 AM

Dave, Thanks for the link- very informative. Up until now I've been scared of any alignment procedures, as a lot of the sources (on the internet) say best not to touch, as you may only make a working set non-functional. In this case, I have nothing audio to lose. I also have the same Heathkit signal generator and my DVOM has a frequency function I can check it against. My signal generator has no leads, so I built some using shielded audio cable and test lead clips (Radio Shack is still useful for something outside of cell phones!).

One thing I didn't quite understand. You mention the connection between the signal generator and the tube on the tuner (we have the same tuners), but you mention putting cardboard by the tube shield to prevent grounding. I couldn't see how exactly you did this. Can you describe it? Bear in mind I'm a newbie here...

Thanks!

DaveWM · #17 01-05-2015, 09:20 AM

You just want the tube shield not to be grounded, if you can keep it up a bit from the chassis, that is good, I think I used the cardboard to keep a strip of metal from touching the tube shield. The goal is to couple the signal thru the glass of the osc tube, the shield therefore must not come into contact with the chassis which would ground out the signal.

The hardest part of working IF for me is correct termination and cabling from gens to test equipment. You want short leads, and correct termination blocks (at least when looking at band pass from sweep gens).

I think the tuner may have a defined test point that may work better than the tube shield, check the riders. I do think its not as critical when just doing a single freq peak (unlike the sweep gen and scope when you are trying to analyse a trace).

and using the long fibreglass rod helps, just moving around the set can damp out signals and change tuning, you notice that as I peak up the last coil near the tuner.

old_coot88 · #18 01-05-2015, 10:00 AM

A turn or two of hookup wire wrapped around the mixer tube, taped securely, is a good method of injection in lieu of the ungrounded tube shield, which may be prone to over-coupling.

UberVacTuber · #19 01-05-2015, 07:18 PM

An update. I remembered that when I was working with this set a few years ago, I would get a better audio response from a VCR rather than a DTV converter. I connected up the VCR and with the contrast control all the way up, I could hear faint audio under the interference. Since the chassis is in the cabinet, I did a rough "ear alignment" (as Phil calls it) and was able to get a sizable increase in volume. (I only adjusted the top two coils, as the third is accessed from the bottom. I will adjust this one as well when I pull the chassis back out for the formal instrumented alignment) The first IF coil has a silver mica cap in it, while the second uses a tubular ceramic.

This reminded me of a quandry I was dealing with back then: If I used a DTV converter, I'd get a nice picture, but no sound. (Even with the contrast turned all the way up, which functions more as a gain control in this set, the sound is absent or very faint. The contrast is set around the middle of the range to get a good picture with no distortion or retrace lines.) If I used a VCR, the sound signal is stronger, but with the contrast dial turned to a point where the audio is a decent listening volume, the video is overdriven and distorted. I wish I could get the good video of the DTV, but the sound of the VCR... Any ideas as to what else I should be looking for? (Yes, I have the sound control on the DTV converter box turned up to the max) I also want to put a signal directly through the amplifier in the lower chassis and verify that nothing has weakened in the main amp itself.

DaveWM · #20 01-06-2015, 10:14 PM

Blonder Tonge AM60 modulator, far better than anything coming out of a VCR or converter box

DaveWM · #21 01-06-2015, 10:27 PM

Blonder Tongue AM60 modulator, far better than anything coming out of a VCR or converter box

UberVacTuber · #22 01-08-2015, 06:09 PM

Are there any other modulators out there that work well? I looked at the AM60, but it's kinda pricey...

Phil Nelson · #23 01-08-2015, 11:56 PM

Many of the B-T agile modulators listed on eBay are overpriced, but if you're patient, it should be possible to find a more reasonable one. I got one for $26 + shipping.

I just did a quick search and there's one listed with a current high bid of 99 cents. Another with a BIN price of $39.95.

Regarding digital TV converter boxes, on mine the audio is just plain weak. I got a little more by switching it from stereo to mono, but not much. Perhaps others are not like that . . . I only own one.

Phil Nelson

Electronic M · #24 01-09-2015, 01:09 AM

If I can get a BT mod delivered for under 50$ I consider it a good deal. With a properly (home) made antenna they are worth every cent of that price IMHO.

UberVacTuber · #25 01-09-2015, 08:13 AM

Thanks for the tip, Phil. I was looking at the B-T website, where they sell for a grand!

Are there any particular features I should look for?

UberVacTuber · #26 01-15-2015, 02:07 PM

Well, I finally had the time to pull the chassis back out and go through the process of peaking up the sound IF stages. The sound is so much stronger now! I can even use my DTV converter and get plenty of volume, even with low contrast. Thanks to all for pointing me in the right direction and the links to the how-to videos. This was the first TV I've ever done and it has been (and still is) quite a learning experience.

One odd thing I noticed: when peaking the upper coil in the first stage, I would approach the peak and just before getting it there is a sudden drop off. When I turn a bit beyond it, the voltage comes back and I get the sweet spot. What could be causing this? I turned the core back and forth and I hit this drop off every time...