Univox U45B

Well, strictly speaking, it's a Radioshack Realistic-branded amp, but it's a U45B. It short it's a plain-looking 10 watt amp utilizing 6BM8's and a 12AX7 dual triode, as well as a 6x4 rectifier. The tremolo does not work as the caps in these are known to leak dc. Looks like a fairly big order to Hoffman is in order, as I have some other bench work to take care of.This amp projects the electrons through a late sixties Mutter Co. Jensen. Not very well thought of, but I happen to have a 12" Jensen, courtesy of the capn. Looks like I've found a home for that.
The upshot of this meandering is, this is a nice amp, that will be made nicer after I recap it and replace the trem caps. You can get crunch at a marriage-prolonging volume, and it cleans up nicely when you roll back the volume. This is a great recording amp, you can just feel it. Pics tomorrow, but I'll warn you - coasties amps are helluh prettier.

Gotta see pictures!

My first reasonably good guitar came from Radio Schack in 1967 ('68?), a Realistic-branded Aria/Conrad ES-335 clone. good guitar, still kick myself that I sold it.

That year they offered two guitars (mine was the lower, the upper was a full Aria Diamond with all the MOTS), a violin-shaped bass, an organ (think Ace-Tone) and ONE amp...yours has to be that amp.

Always though it to be solid-state, so it was really tube? WOW

OK, can't print it or copy it, but go to this 1969 catalog link, then go to Page 77

http://www.radioshackcatalogs.com/catalogs/1969/

I don't ever remember three amps...perhaps my local store never got all three...they had the guitars and one guitar amp, which I would say was the small one...certainly not the twin twelve!

I worked at our local store and then the owe in the next city through high school and my college years...'69 - '74... We had a helluva time finally getting rid of the last guitar (the $89.95 model...had MOTS instead of the black trim)

That's the amp, the little one.

Catalog pic of default's Radio Shack/U45B on the left, pic of the chassis of an early Univox U45B proudly displaying its Asiapan origins; use of electrolytics caps in the signal chain (gray/silver gadgets on the left side of the circuit board) and - a little less visible - open, accessible lugs on the bottoms of the transformers. Note the very respectably-sized black output transformer in the right center and 'D' luggage handle ... the same style used on the first generation Guild T1 RVTs. When this is fitted up, we gonna see default Climbing the Stairway to Heh-ven ... 8)

Not only is that a cool amp, it's a cool piece of Americana as well. I might have to get me one of these, as the ones I have now are too loud!

capnjuan said:

When this is fitted up, we gonna see default Climbing the Stairway to Heh-ven ... 8)

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I used to be a roofer too! Unfortunately, I had a bad habit of stepping back to admire my work... :roll:

Am I correct that there is only one preamp tube? Ah, gotta love low-gain Guilds! All the distortion must come from the power tubes...sweet!

Hi Bill; yes, single 12AX7 along with two 6BM8s, and a 6C4 rectifier. It's the same circuit as the late '50s Gibson GA8T. It also shows up badged 'Meteor' built in Asiapan and possibly distributed by Hilgen. The 6BM8s sound a great deal like 6V6s but can't run at higher voltages so these are usually limited to 10 watts. Great amps; like the Silvertones, lots of tone for the money.

Sooo...

How did the little RSC amp turn out?

I've had distractions. Some parts came in for it and John Kidder's amp. I'm planning on spending quality time with John's this week.

twocorgis said:

Not only is that a cool amp, it's a cool piece of Americana as well. I might have to get me one of these, as the ones I have now are too loud!

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There is one on the bay right now...

http://cgi.ebay.com/VINTAGE-CAVALIER-UN ... 596wt_1141

I'm guessing It will sell pretty close to the $149 starting bid, if at all...

After I get John's amp up and out, I need to give the RS some love. I'm planning on recording an album for the RPM Challenge this year and I need to service most of what I own. :?

I've owned several of them they scream

Top chassis next to the Realistic amp (tips hat at cj for providing pics) is the typical Univox branded U45B. The below pic is the chassis of my amp. Because the chassis sits in a Fender orientation (horizontal) the power tranformer is jammed into the chassis. I changed out all the electrolytic caps, added a grounded three prong cord and replaced the exposed fuseholder with the more typical enclosed fuseholder.





Blue and orangedrop capacitors replaced the oil-filled Nipponese oem Atlas caps and now the trem works.


I like tremolo!

Default said:

... I like tremolo! ...

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Love the hat ... and the amp! 8) 8)

Default said:

I like tremolo!

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Steve, you handsome devil you! How's the house coming?

Played my son's Tele through it yesterday and wasn't impressed.

Then I realized the strings were three year old flatwounds.



Yow! What a great sounding rig. :shock: It was supposed to be a "service and resell", but I'm really torn between cashflow and gear greed.

Couple on ebay now. The one in Hawaii might not see much interest, due to the 80 shipping.
Like cj said, they were sold under a variety of names, so look for construction and tube lineup and maybe you could steal one too.

Bill Ashton said:

Am I correct that there is only one preamp tube? Ah, gotta love low-gain Guilds! All the distortion must come from the power tubes...sweet!

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Hi Bill; I think I mis-bungled my earlier reply. In one sense, the amp only has one preamp tube - the 12AX7 - but the 6BM8s, cousins of the 6GW8, are 2-fers ... two tubes in the same bottle. In the lower right-hand corner, that's the diagram for the 6BM8; there is no interior partition but it's a triode half (like half of a 12AX7) together with a pentode ... an output tube but only requiring one tube socket for the two different functions. In the U45B, one half of the 12AX7 is the first gain stage seen by the signal. The other half of the 12AX7 (in the lower left [red boxes are the trem caps that Steve replaced]) is the tremolo oscillator. In the upper center, you'll see the two triode halves of the 6BM8s; the first acting as the recovery after the volume and tone controls and the other, the phase inverter for the two 6BM8 pentode halves ... the output sections. So ... the preamp is half of a 12AX7, half of a 6BM8, and a phase inverter/driver.



In Gibson's tweed GA8T, they used one of the 6BM8 triodes for the trem oscillator and left other half of the 12AX7 as the post-volume recovery stage. The 6BM8 was widely used in post-war European table radios; a good trade-off between tone and, because it saves another tube socket, manufacturing economics. I don't know when the 6GW8 showed up but there are far fewer premium Euro versions of it than there are 6BM8s. A few years ago, Electro Harmonix brought the 6BM8 back; do not know if they are still supporting it. A very good-sounding tube easily mistaken for a 6V6; golden brown honkers !