Hallicrafters parts

[rainedave]

I have this old Hallicrafters 5R10A radio. Are there any parts in here that have a use in guitars or amps?

Thanks

[syrynx]

You could probably make the equivalent of a Silvertone Danelectro amp-in-case unit out of it. Like those amps, the receiver uses a series filament string, because, like those amps, there is no power transformer. Here's documentation of a 5R10A restoration which explicitly spells out the danger inherent in this design. If I were doing it, I would plan on using an isolation transformer to avoid the danger. Here's a PDF of the 5R10A manual (2 MB download), which includes a schematic.

[rainedave]

Thanks syrynx. Those are great links. So, do I understand correctly that the 120v AC flows straight into the circuit, through the rectifier tube and filter caps? What does the filament string do? Does it change voltages for stuff like the heaters, etc? Converting something like this into an amp is many, many levels beyond my abilities.

According to the manual you linked to part #C-9 is a .05 MFD 200v paper cap. Would that work in place of the .047 MFD cap in my Esquire? If it's still good it might be cool to have a 59yr old cap in there.

Thanks

[rainedave]

OK, the first thing I did was remove the 2-prong AC cord so no one will plug this thing in and hurt themselves. The two AC wires were soldered directly to the rectifier base. The wall current went straight into that tube.

Then, using the schematic in the manual I located the .05 MFD cap and removed it (it can always be replaced). Here is a pic of it. It's a Sprague .05 MDF 200VDC paper, wax coated cap.

I don't have any way to test a cap other than to check for continuity which gives me an "Open" reading. So, I don't know if this cap is still within spec or not.

[big-daddy-59]

Well, a correctly functioning cap should have NO continuity,so that's good. A shorted cap would show continuity, and that would be bad. And be sure to save that cap. You can use it for a "boteek" tone cap in a guitar.

[rainedave]

Originally Posted by big-daddy-59

Well, a correctly functioning cap should have NO continuity,so that's good. A shorted cap would show continuity, and that would be bad. And be sure to save that cap. You can use it for a "boteek" tone cap in a guitar.

Thanks. Yes, that's exactly why I removed it. I want to replace the .047 in my Esquire with this one if it will fit in the control cavity.

[syrynx]

Originally Posted by rainedave

OK, the first thing I did was remove the 2-prong AC cord so no one will plug this thing in and hurt themselves. The two AC wires were soldered directly to the rectifier base. The wall current went straight into that tube.

VERY good move! :)

Originally Posted by rainedave

Then, using the schematic in the manual I located the .05 MFD cap and removed it (it can always be replaced). Here is a pic of it. It's a Sprague .05 MDF 200VDC paper, wax coated cap.

Another good move. :) The worst that can happen in your Esquire is that you don't like it.

Originally Posted by rainedave

What does the filament string do? Does it change voltages for stuff like the heaters, etc?

The tube filaments (heaters) are wired in series, exactly like old style Christmas tree lights (so if one fails, they all go dark). The first two digits of each of the receiver's tubes indicate its heater voltage: 12SA7, 12SK7, 12SQ7 = Detector and 1st Audio Amplifier, 50L6, and 35Z5. Add the numbers; (3 x 12.6 =) 37.8 + 50 + 35 = 122.8.

Originally Posted by rainedave

Converting something like this into an amp is many, many levels beyond my abilities.

B-b-but it's already an amp! It merely happens to have a medium- and short-wave tuner connected to it. ASSUMING THAT IT WORKS, and ASSUMING THAT IT IS CONNECTED TO AN ISOLATION TRANSFORMER RATHER THAN THE AC LINE CORD, all you'd need to do is disconnect C13 (.01, 600V) from R9 (the 2 meg volume control), connect the tip terminal of a 1/4" jack to the volume control, and connect the sleeve terminal of the jack to ground.

It would be a painfully inelegant amp-- low power (probably no more than a watt, given the low plate voltage), with no tone shaping (except the loss of highs in C11b and C15), and two useless tubes soaking up power while contributing nothing except resistance and continuity in the heater string. But there is potential (sorry! ) for coolness here. The audio section could be tuned to something much more guitar friendly. The 12SG7 could be reconfigured as an additional or alternative gain stage. The 12SA7 could be reconfigured as a tremolo oscillator. At the very least, you could have a tube amp suitable for practice and recording levels for the price of an isolation transformer (and probably new power supply capacitors).

Thinking out loud here, my own inclination, if it were mine, would be to forego the extra gain stage and tremolo, strip the chassis of everything NOT the audio amplifier, and use the chassis real estate gained for an isolation transformer. I'd pull and pitch the can cap (C14a-d), replacing with discrete electrolytics (as was done in the restoration project linked above). I'd have to calculate the resistance and power dissipation requirements of the ballast resistor needed to compensate for the loss of the two tubes I'd remove. I might well end up rewiring the preamp tube (12SQ7) socket to use the 12SG7 as a higher gain preamp.

It would be possible to strip the chassis of everything save three octal sockets, and use it as a foundation for a Champ clone or something similar. But that would mean hefty investments in power and output transformers, and the Champ tubes would be far more expensive than replacing the three I'd probably use from the 5R10A.

As I type this, I'm looking at tube prices from popular online suppliers:

• NOS 50L6GT: $8.95 (less than a 6V6...).
• 12SG7 USA Tube: $5.45 (less than a 12AX7...).
• 12SQ7 USA Tube: $11.45 (more than the least expensive 12AX7s, less than most, but more than double the 12SG7 from the same vendor...).
• 35Z5 GT USA Made NOS Tube: $8.45 (far less than a 5Y3...)

I hope this is enough information to let you decide whether attempting to make a silk purse out of what, IMO, is a sow's ear is a project you'd like to tackle yourself, or whether you should charge someone else for the privilege.

If you decide you may be interested, post again, and I (or, with luck, some of the many folks far more expert than I) can offer suggestions about isolation transformer solutions and the least dangerous ways to test what you have.

[rainedave]

Thank you very much for all of that info John. It does sound like it could be a fun (and challenging) project. I'm just going to leave it be for now. But, there's a place here in my town that specializes in converting PA amps for guitar and harp use. I might talk to them about this radio and see what they would charge:

http://www.djlservice.com/PAAmpConversion.htm

The scary thing is that a couple of moths ago I had the thing plugged in and was listening to radio broadcasts through it. So, it is (was) in working order. One weird thing about it: the volume control is the on/off switch and it worked backwards. When I clicked it on it was at full volume and as I turned the volume knob up the volume went down, so something was wired wrong. Also there was a lot of scratchy noise when turning the knobs. I read in another post that that could indicate DC voltage on the pots.

I removed the Sprague .05 mfd cap and used it to replace the .047 tone cap in my parts Esquire. The middle position on my Esquire uses the tone control and with the tone all the way up it has slightly less high end that the back position with no tone control. It's just a little bit warmer. I can't really say that I can tell a difference in tone between the old Sprague and the original Acme cap that I took out, but it works perfectly so I'm leaving it in there.

[syrynx]

It's nice to know that the radio worked a few months ago. That means that you re-formed the electrolytic capacitors, so they should still be working if you decide to test the radio in amp mode down the road a few months (or even a few years.)

The backward volume control wiring can easily be fixed. The scratchiness could be DC on the pot, or it could just be the scratchiness any audio pot exhibits after being neglected. (I have way too many of those!)

The capacitor seems to be working exactly as a good tone control cap should; cool! :)