Miller Quality Products 570-T - Videokarma.org TV - Video

mr_wetland · #1 04-08-2009, 04:31 PM

Anybody know anything about this beastie? I picked it up from a guy cleaning out his barn. The only info I can find on it says it is a "high fidelity tuner", ca. 1937. It seems to be complete, although I'm pretty sure the original transformer has been replaced. I'll try to post some pix later. Maybe it's actually a mono tuner that belongs in the tube audio section rather than antique radios, but if anyone knows of this I'd appreciate some info. I haven't plugged it in and fired it up yet because I don't want to blow anything up...

Steve

toxcrusadr · #2 04-08-2009, 11:31 PM

1937 is way too early to be considered a 'mono audio tuner' - that's strictly postwar in my book. Looking forward to pics!

Tom Bavis · #3 04-09-2009, 07:56 AM

Sams lists a J. W. Miller model 560 (1959) and 580 (1961)

(edit) 1942: http://www.indianaradios.com/Miller%...AM%20Tuner.htm

Earlier version: http://fmamradios.com/Miller570.html

mr_wetland · #4 04-09-2009, 09:36 AM

Thanks, Tom. 1942 it is. Here are a couple of pix. I'm trying to figure out if the output transformer is actually missing, or if someone replaced it with that little silver box. I haven't had a chance to take it apart yet. I am very curious as to what this thing does. Reading that article about the kit, it is very interesting to think it might have been state of the audio art at the time. I am also very nervous about firing it up. I don't have access to a variac and haven't built a "poor man's" yet.

Reece · #5 04-09-2009, 11:51 AM

I wouldn't fire this up yet. Might blow something hard to replace, like the power transformer. Might want to follow this procedure to be sure the power transformer is OK before going ahead.
1. Pull the rectifier tube. Make sure the power cord is OK and with the unit unplugged and power switch turned ON check ohms across the power plug prongs to be sure you don't have a dead short.
2. Leave the rectifier tube out. Leave the other tubes in. Connect the radio in series with a lamp socket and put a 60 or 75 watt bulb in the socket, then plug in and turn on the radio. Bulb may light dimly. If it lights full brightness, bad news. If it does light dimly, leave it on for a while and watch (and sniff!) the radio. With the radio in shadow you may see tubes lighting up some. Stay with it for ten or fifteen minutes watching all the time. Feel the power transformer: it may get warm but should not get very hot.
3. Next remove the 75 watt bulb and put in 100 watt, repeat as above. After fifteen minutes, if your transformer is only warm, and most tubes are lighting, good news!
4. This set is wide open and the paper caps are easy to get out. Change out ALL the paper caps under the chassis and install new electrolytics under the chassis, leaving the cans on top for appearance sake.
5. Clean everything up, clean tube pins and sockets, tubes are good most of the time if they light. This is a tuner so won't drive a speaker but would drive some 'phones, or would drive a powered computer speaker, just for testing. Let 'er rip!

Hope this all hasn't been too obvious, if so, sorry!

Reece

toxcrusadr · #6 04-09-2009, 12:26 PM

Good advice. In the absence of the light bulb gadget I've been known to just proceed with recapping and things usually work, but if you have a bad interstage transformer etc. you might do all that recapping for naught. The light bulb gadget is pretty easy to build and cheap.

mr_wetland · #7 04-09-2009, 01:36 PM

The procedure makes sense and is all sensible. However, in my newbie-ness I am not sure which is the rectifier tube. I have the following tubes - two 6D6, two 76, one 6B7, one 80, one 6G5. The 6G5 seems to be the glow light that comes on to tell you you're tuned into something, that's under the chassis. Everything else is on top. Sine I'm trying to learn as fast as I can, what does the rectifier do? Is it the same idea as a diode, allowing current to only flow in one direction?

Regarding the caps, only one of the cans on top is a capacitor, the rest are coils. The schematic seems to show them as being 8mf, nothing about voltage. These are high voltage, right? I can read most of the writing on the paper caps, low capacitance, high voltage. Those I can replace. Anybody have any insight about my output transformer situation? The schematic says I need a tube to line transformer, model T-62-A-26, which is not there. There is a small cardboard wrapped box under the chassis that is wired as if it's the tranny, but I haven't taken it out yet to get any info off it. I'd like to put the tranny back on top where it belongs. Any idea what I need and where to get one? Thanks as always for the help, gents.

Steve

jeyurkon · #8 04-09-2009, 04:49 PM

The 80 is the rectifier.

John

mr_wetland · #9 04-09-2009, 05:00 PM

OK, I see that and it comes right off the PT. Does that convert AC to DC? I hate to sound ignorant, but what does it do?

mhardy6647 · #10 04-09-2009, 05:52 PM

that's what it does.

Reece · #11 04-11-2009, 11:58 AM

Testing with the ohmmeter and the light bulb in the beginning, with the rectifier tube out, is the way to test the power transformer for shorts. If there's a short in that, you're in for a relatively big expense and you may decide that the set either is or is not worth fixing at that time. It's easy to do that now at no cost rather than recap and find out the bad news later. At least you know where you stand going in. When the bulb lights "dim" you let out a big "phew!"

Reece

mr_wetland · #12 04-11-2009, 11:57 PM

Thanks, Reece. What exactly am I putting the ohmeter on? The PT and choke look okay, but I'm sure that doesn't really mean anything on a unit this old. I am learning as I go, but need a little (a lot?) of hand holding at this point.

Regarding my output transformer issue, I still haven't gotten any response on that. The OPT is gone, and I need to find a suitable replacement. Any ideas? The original parts list calls it a "tube to line transformer" without giving any voltages. Once I get the OPT in place, I'll do the re-cap (what the hell, it's good soldering practice) then try firing it up and see what happens. But a liitle schooling on where I'm checking for resistance and voltage would be a huge help. If any more pix would help, let me know.

Steve

Reece · #13 04-13-2009, 12:19 PM

Have the unit unplugged and the power switch turned ON. Take the unplugged plug (!) and clip the ohmmeter probes onto the prongs of the plug. Set the meter on lowest ohms. You are looking for some low ohms reading here, maybe between 3 and 10 ohms, exact number not important. The important thing would be that you don't see zero ohms or something really close to it. That would mean you had a shorted transformer primary, or that the .1 mfd. caps are shorted that are connected from each side of the transformer primary to ground. You can test across each of those also to check for shorts should get infinite ohms.

I'm betting that the power xfrmr. is OK and after the test above it's time to do the light bulb test as outlined before.

As to your output transformer, I think you can get along without one. The original circuit was meant to be used in a studio or similar "back in the day" with 500 ohm line output. You'll probably be connecting this to a home amplifier in mono mode, and it could be done with a resistor/capacitor circuit. In the bottom right hand corner of the blueprint schematic is shown the 76 output tube and the original transformer. If you could sketch and post what that circuit looks like now it would be helpful.
Thanks!
Reece