[TV MAN]

So this simple little amp should be a simple little recap, right? Hummm... not this one. This was an eBay find several years ago sold as a "guitar amp". It works, but hadn't used it for some time. I decided to get it running since all it should need are caps and it will work fine ... yeah! As you can see in the pics, the recap has been completed. I'm sure those 2 sand resistors need to be replaced also, 120 ohm, then there's 2 coils off those resistors, not on the schematic. Those go off to the plug on the side of the chassis. Maybe to the phono motor or something. BTW, I DO have a nice 557 I want to restore. I'd thought of just swapping amps and calling it good, but not gonna happen. So what is wrong with this little amp? Well, a little bit of everything! I never get the same sound twice and it just doesn't sound right. I've checked voltages and signal traced without much success. I finally did spot a place on one of the output tube sockets that I saw arcing - to the beat of the music! I cleaned the sockets and ... it got worse. It even started smoking to the beat of the music when I really pushed it. Oh, now I've lost part of my B+ voltages - actually, it just dropped off, and really can't find a reason. So, I'm going to have to pull things apart and replace those 2 output tube sockets and check connections. Oh, I did find a cold solder connection on the cathode of the output tubes, fixed it and still wont behave.

Here's an interesting note ... back when I was a youth in the '70's, I had a VM 557 given to me - actually, I kinda took it. Was my mom's from her high school days in the '50s. Stand and all. I played that thing and played that thing. Loved it. But, like all things, it started to give trouble. It ALWAYS has a hum/hiss in the sound and would sometimes just up and shout out a nice feedback whistle. Mom said it would do that - since new! But, I still loved that old phono! It finally gave it up, volume dropped off, then would suddenly and without warning start blasting. Oh, and for a suitcase record player - that baby would crank! It finally did get so bad that it wasn't really usable so it got taken apart and that was the end. I still remember watching the trash guy throw it in the back of the truck. END.

So, what's so weird is that this amp I'm working on now - exhibits almost the EXACT same problems as that amp I had as a kid! So, I really want to solve this and take notes of just why and what the problems are! Wow! I may even take the original amp out of my present 557 and see how it acts. So, there's a reason I have a 557. It's something from my youth. Something I enjoyed a lot. And missed. So there ya have it. I'll include a schematic, but I'm betting I'm gonna have to completely redo, resistors and all. 

   
   
   

[David]

Time for a stupid question what happens if you flip the plug when plugging in the wall socket? 2nd stupid question have you tried a isolation transformer? I think the NEI changed in 1973 to require 3 prong plugs was something like 1978 before all states said ok. David

[morzh]

For intermittent things...I have a rule: if you have all good tubes, full recap and socket cleaned, it should just work.
Oh...the miniatures, if old, might need some pins cleaning.
Of course, cold solder joints and cracked resistors - could be revealed by light tapping with some plastick stick.

[radiorich]

Hello Tim,
I have a little RCA 45Y-2 that after replacing the capacitors and some other parts it worked but it also started acting up it also uses one of those Sand resistors too plus it has domino mica cap, So I am going to replace both also check for noisy resistors.

Sincerely Richard

[Arran]

Tim;
I was just going to mention the sand resistors, but Richard beat me to it. Those are a replace on sight item with me, they are the only wire wound resistors I have had fail just from sitting on a shelf. They have a habit of corroding, and the connection between the resistive wire and the ends tends to break down, in my opinion they aren't worth messing with. The two 2 Watt carbon com resistors with the rough bodies should also be checked, they don't behave like sand resistors but they do go up in value.
Regards
Arran

[radiorich]

Hello Arran,
I agree with you about those 2watt .

Sincerely Richard

[TV MAN]

Those sand resistors may just be the culprit. I'll swap those and see how it behaves. They looked & checked pretty good, so I didn't mess with them. I did clean the tube pins and sprayed some deoxit on the sockets - that's when it started smoking. I'm betting there's a carbon track between the pins. It's kinda weird to run into this after all these years. I used to see that on TVs, a certain model or brand comes in and "well, it'll those (blank) replaced or have a bad (?)". This little amp is pushing over 350v in some parts. Pretty stiff for a simple phono. 

I'd like to know the history of these. Most of those suitcase phonos where just rectangular boxes with lids and a player inside. This one has 2 speakers, maybe 3 - I think I remember a tweeter, separate bass and treble controls, external input & output. Even the cabinet has a megaphone wedge shape to it, starting narrower at the back and flaring out at the front. This is not your average suitcase phonograph from the era! This one is designed to put out some serious sound waves!

[MrFixr55]

Interesting amp, TV Man.  V-M was no Fisher, but it looks that this was a serious attempt at HiFi. I take that the output tubes are EL84 / 6BQ5s.  These things can outdo 6V6s.  These were likely in the Vox amps used by the Beatles, Kinks, rolling Stones, etc.  These can develop as much as 17W at 300V in Push Pull.  So this is why the amp rocks.

Seems that there are many places for bad things to happen.  What is S7 labeled as?  Seems to be part of the feedback circuit.  (many inexpensive amps did not use feedback.  Wonder that if this switch opens, negative feedback is affected.  Wonder if the thing breaks into oscillation.  New sockets and plenty of Glyptol on the output tube plate and screen connections?  Use ceramic sockets?  Seems that C11 can do funky things if it leaks.  I totally do not understand the phase inverter circuit.  Maybe change it to a cathodyne phase invertor (See your "Classic Dynaco" circuit).

VM did do some strange things, but they DID sound good.  We had V-M 316 that Dad bought for Mom for Christmas 1963.  Mom loved the thing for many years until I came up with better stuff and she lost interest in records.  It deteriorated, the speakers were glombed for the garage, ersatz guitar amps, etc., and of course, the cartridge and capstan went sour.  I should have grabbed the amp before we threw the case out after Dad sold the house (Mom passed away several years before at the young age of 54).  This Phono did a lot with a little.  Stereo phone with volume, balance, bass, treble controls.  No power transformer.  Amp was 2 Single end 50L6s and a 12AX7.  Solid State voltage doubler circuit.  Each speaker cabinet had 2 different 6" speakers.  No tuned port or anything like that.  I suppose that with 180V on the 50L6 plates, the thing developed 5W per channel. 

Had friends who had a Maggot Box OOPS, Magnavox suitcase.  Mono, 8" speaker (can't remember if there was a tweeter or just the "whizzer" cone on a single 8" speaker.  Amp was 12AX7, 2 50C5s and solid state voltage doubler.  The thing did put out. 

Had a Magnavox console with a 24" B/W TV, Collaro changer (I substituted a Garrard with a magnetic cartridge and a radio shack box preamp)  AM FM radio (not MPX Stereo or even AM A FM B).  The power amp was 2 SE 6BQ5s and a 12AX7 with 5Y3 rectifier.  2 old school 12" full range speakers (similar to the ones in early post war console radios) with 3" tweeters.  Sounded pretty nice but boomy.  parted out when the CRT died, was an oddball 24" that I could not sub with the 23" tubes that were in sets that found their way to the street.  Still have the power amp chassis.

Had the power amp from a Magnavox AM FM Phono mono console.  1 12AX7 driving 4 6V6s.  Brother in Law had a similar set but he trashed it before I could get the amp chassis from it.  My amp chassis was long gone but I saved the output transformer from it.  Shame, that could have made an impressive amp.  But I DO have 2 Bogen Challengers.  One has 4 7868s, the other has 4 7591s.  If the output transformers are the same, this would make a great Stereo Amp or 2 "MonoBlocks".

And all the others that got away, especially when Dad ordered a "purging".