Tube amp Theater Univox Lafayette guitar amplifier U-320 How to fix upgrade

[@DeWittPotts]

Lafayette Radio Electronics Corporation was an American radio and electronics manufacturer and retailer from approximately 1931 to 1981. Headquartered in Syosset, New York, the company sold radio sets, amateur radio equipment, citizen's band (CB) radios and communications equipment, electronic components and tools through retail outlets and by mail-order. They used to have an outlet in Kingston, NY which is where I discovered them back in the late 1960's. Like Sears and Montgomery Ward they sold rebranded musical equipment such as guitars and amplifiers.

[@confusedbyzebras6348]

I have this amp and it is dull for guitar but works great for bass. Love the apology to collectors line! I could see them clutching at their chests!

[@smstiao-tecnologia]

Do not worry my friend, your videos are very inspiring to all of us technicians in electronics and especially those working with electronic tubes. And sure Terry does not think there is a better sound than those of our electronic tubes. Strong hug to everyone !!!

[@frankgeeraerts6243]

Hello Terry , you're right...............those Russian ( fake) 7591's were cooking and indeed you couldn't get the current lower with a bias voltage range in this amplifier that was originally build to run with the genuine nos 7591's .. In fact .......The Sovtek stuff does look very similar to a standard Russian 6P3S-E. Given that Ebay was pretty flooded with this tube, I wouldn't be surprised at all if a lot of re-marking is going on. The phrase "all you have to do is change a resistor" should read "all you have to do is redesign the bias and drive circuits". The 7591A was special in that it had a high transconductance. This is a blessing in that it's easy to drive. It's a curse in that the grid is closer to the cathode, making shorts more likely and grid emission more of a problem as well, as the control grid cant help but be heated up by the cathode if it's really close. The classic 6L6 tube requires MORE negative bias for a given bias current, and more drive level for a given output than the higher transconductance of a 7591, so you could have almost no output power with the fake 7591's, making me suspicious/convinced that the Sovtek 7591 XYZ are re-marked surplus tubes. I heard lately that JJ seems to produce a better copy of the 7591.......... The nos 7591 sounded very different than a 6L6 . Happy you found a good working solution for the amp besides the necessity of trading the sound of an obsolete tube type for a 6L6. Only when one has stock of the original 7591 , original restoration might have be considered. I had stock of 7591 tubes made for organ , labeled RCA but made by Westinghouse , helped some desperate audiophiles with old receivers and amplifiers . One tube type is an exact equivalent for the 7591 but with another basement/pin out ....................i think it was the 7868 , but it is also obsolete nowadays ..... Have a nice day and thanks for the uploads and your healthy & fine humor.

[@goodun6081]

Frank Geeraerts, you are correct in that the 7868 is internally exactly the same as a 7591, but it has a Novar pinout, which is nine skinny pins arranged in a semicircle but the total diameter of the semicircle is larger than it would be for let's say a 12 ax7 or el84. Vintage 7868 tubes are somewhat more common and somewhat less expensive than vintage 7591, and It is quite possible to replace the octal sockets in a 7591 amp with Novar sockets, if you can find them (online, or cheaper from a hamfest, or perhaps even pull them from an old tube type television). I have made my own 7591 to 7868 adapters , but it's not an easy thing to do and I have never seen a commercial product for this. However, There is also a tube known as a 6GM 5 that is the same as a 7868 or 7591 internally, but it has the same nine pin base styling a 12 ax7 or el84 ( different pinout, of course). I have seen commercially made adapters that can convert a 7591 socket to use the 6GM5 tube instead.

[@accorgan]

This amp is a Univox U-320, I have one in a piggy back and separated speaker cabinet with 2 12" Jens and high freq horn in it. From My understanding Univox made amps for Lafayette Electronic and I also heard Radio Shack. The design are the same and circuit board are the same. I have the Univox U-320 and the output is about 25 to 30 watts.

[@accorgan]

That is a Univox U-320, I have the same amp made by Univox. Univox use to make amps for Lafayette Electronics and Radio Shack back in the 70's. When I got my amp they say it was 60 watts, but when I blew the output transformer, I learn it was 60 watts peak to peak and was only 25 to 30 watt amp. It was good amp for me.

[@mikesradiorepair]

Nice to see I'm not the only electronics guy with a machine shop. I would be lost without my Bridgeport. Nice conversion on the amp.

[@d-labelectronics]

+MikesRadioRepair .CBRadio Thanks Mike. It was an all day project. As you can see, I started the job with coffee and ended up with wine! I have a few Bridgeports at my day job, but can afford one at D-lab

[@gflanagan]

Thanks for making this video. I just got one of these (Univox U-320) on the bench to check out for a friend. This video got me up to speed quick!

[@kaypolo]

Univox. I have an early 60's Univox and it sounds great. It breaks up real well. I got it for free.

[@smstiao-tecnologia]

Good job Terry this amp, your modifications were very good, the vezez is necessary to improve radicalize !!! Congratulations once again for his fine work, and I liked the shirt of D-Lab. Good end of the year to you and all of your blessed family !!!

[@d-labelectronics]

+Sebastião Souza Thank you my friend. I promise to have more videos like this soon. I appreciate your faith in me + kind words. Terry

[@bootlegapples]

My u45b's caps were mostly all leaky-same brand,they are notorious for that.I swapped them all out,the tremolo now worked it had more volume and the loud hum disappeared.IMO it would have been best to leave the stock transformer and chassis as is and just replace the caps- a less invasive procedure on a *vintage* amp.

[@AndyWragg]

Love the wine drenched intro's and epilogues. Great video Terry.

[@d-labelectronics]

+Andy Wragg Thanks man, I try to keep the cheesy appeal.

[@AndyWragg]

+Terry Dayton I just this evening finished my JTM 45 clone. I'll get some videos done soon. Just relaxing with a glass of rioja.

[@raymondlau6507]

Hi Terry, I checked the tube data sheet on the 7591, and the cathode was on pin 5, not pin 8 as the 6l6gc is. This could be why they behaved so strangely

[@theanthonyrw]

Once again Terry, You amaze me. Why do you have to be so far away from so california. I have an SWR750 that needs to be fixed. WHAAAAAAAA!!!!!!!

[@TheGalaxyhopper]

bias? hmmmm, I wish, I knew more electrical "theory"-Love the channel!

[@daveogarf]

LOL! "Mill-y Vanilly"! UP TOP! 'Caplacitor' - also great! 'Rectumfier' - the BEST!

[@jeffellingson373]

Great Videos D-lab. where is the bit of video with your player?

[@jasonbrindamour903]

I like what you do and what you know. I also like to learn electronics, electrical, welding, soldering and so on....I have a few old tube amp I want to work on which is why I came across your vid...but what I noticed was your music...was that a Blue Light Orchestra(I think) released from Tel Arc? It sounded much like that version I have....

[@wfry7357]

Great vid. Should switch from Petite to a Cab with the transformer change! Was the board a "MUSCAL AMPLIFIER" board? I've got a noname "MUSCAL AMPLIFIER MODEL H 43.2.16" in a combo cab with 2 12" Jensen, Japanese 7591 for power, with reverb tank and a tremolo. Thought I saw the MUSCAL AMPLIFIER on the board ?

[@vacantjosh]

I actually just lucked into one of these amps for very little money. This video is the best info I have found on this particular model. Thank you SO much. I have a couple of questions though if you don't mind. A. Are all of the preamp tubes 12ax7's? Mine had 3 12ax'7's, a 6AN8, and a 12AU7. What kind of issues would incorrect preamp tubes have (it would be amazing if you would check out the videos of the amp that I posted on my KZbin channel, and offer insight!! I'm kind of broke at the moment, but if you can offer any help, I'll gladly make a donation on your website as soon as I'm able! No BS! I promise I really will!

[@BenPrevo]

Nice but those 2 C12R's wont handle the output ?

[@brittisaacrossman]

Good afternoon, Terry! I have a similar amp problem with my screen voltage going a few volts higher than the plate when it's loaded down. Unlike your situation, however, I am able to change the bias, and have got the pair of 5881's to about 32mA each with 445 volts at the plate, giving 14-15 W or ~65% idle. And yet, my screen voltage is higher, despite going through a filter choke. Do you have any idea as to what might be the problem?

[@d-labelectronics]

Hello, does your amp have screen resistors? This one did not. I added a 1K, 5watt resistor in line. Screens look A-ok now

[@brittisaacrossman]

Yes, I have 470R 3W resistors... Maybe I should raise these? It just seems strange that the OPT would be dropping more voltage than those resistors...

[@joeturnip4216]

You crack me up !!

[@BriBlack68]

"It's not French but it's fried" hahaha !!

[@juniorkong9587]

Right on bro!!

[@slaznum1]

Good stuff

[@danpeabody5687]

I am asking everyone I can I figure I'll ask you you work on a weird amps you ever heard of a Sano stereophonic amplifier guitar amp 2 12 s black grill cloth weird gold swirls on it probably about 30 Watts it has no markings other than it says 5363 on the amp chassis

[@d-labelectronics]

Is it tube type?

[@danpeabody5687]

D-lab Electronics yes it is tube

[@goodun6081]

dan peabody, Sano specialized in amplifiers for accordion useage; some have them may have been built by Ampeg or former Ampeg workers and engineer's who split off from the company. the couple of Santa's I have heard pretend to be very clean sounding and would probably be best either for jazz guitar or for use with effects pedals. a stereo Santa lamp might be nice for setting it up to sound like a magnatone stereo amp with the addition of some kind of vibrato pedal.

[@rush2795]

we're gonna play some crazy music! I'm expecting slayer or some shit, and get dracula haha

[@tomcurrie7249]

A whole lot of unnecessary work.