Flot-A-Tone, of unknown model............

[Jack_Hester]

While I was out in the shop this morning, beginning my Spring cleaning, I decided to pull out an old amp that's been sitting for quite some spell.  It's a Flot-A-Tone, but I have no history on it.  Nor do I know the year or model.  I didn't plan to tear into it today, but I did want to put it on the lamp limiter to see what happened.  Here's some pictures of it sitting on top of my Generac: 







When I powered it up on a 25 watt bulb, it came on immediately, no matter the power switch position.  I didn't go any further with higher wattage lamps.  I need to explore this issue before doing more. 

It has 4 inputs.  Inputs 1 and 3 are phone jacks, and 2 and 4 are microphone jacks.  It has three bare braided cables going from the amp chassis (in the bottom) to the control panel (on top).  I don't know if these are original to the amp, but I like the looks.  It may be missing one, but I won't know until I have it all apart. 

Anyway, I'll work on this project and the '59 Harley ( http://el34world.com/Forum/index.php?topic=20258.0 ) at the same time.  I figure they will both be done by Summer, the bike probably first.  I'll post progress as I'm able to.   Have a good one. 

Jack

[TIMBO]

Looks interesting Jack.
What is the white metre on your power supply???

[shooter]

Nice amp!

What is the white metre

looks like a Watt-O-meter, used to monitor AC amps, power, volts.
Handy to have, but don't use it on a modified square-wave invertor, It killed mine!

[Jack_Hester]

That's what it is.  I like to watch the current draw when I'm troubleshooting.  If the power issue is the switch, I've got a short-bat switch that will look appropriate.  It needs a new cord.  I'll leave this one on, while troubleshooting the switch. 

Jack

[HotBluePlates]

I think your tone will be at Maximum Flot once you get that thing sorted!!

[Paul1453]

Looks like PP 6V6s with a nice octal pre-amp.   

Maybe 6SN7 or 6SJ7s in the preamp? 

[HotBluePlates]

Looks like PP 6V6s ...

I'm gonna guess those are push-pull 6L6's. And a 5U4 rectifier.

Preamp tubes will be wild guessing, but I'll say probably a 6SL7 input tube and a 6SC7 phase inverter.

[Paul1453]

You are probably right HBP.   

They do look fatter than 6V6s now that you mention it.
I can't seem to get a good close up look.
Seems to be a field coil speaker too, No? 

[Jack_Hester]

6SL7
6SJ7  6SC7
6L6 x 2
5U4

Still haven't found a schematic with this tube lineup.  But, it shouldn't be difficult to create one. 

Both the microphone cables have been cut, but I assume they were wired to each of the volume control pots, like the instrument inputs are.  One of the instrument input grounds is unattached.  Other that these discrepancies, it appears to be an easy fix.  We'll see.  I plan to mount a solder terminal strip to one of the transformer mounts.  Then, land the new grounded power cable to these terminals.  I don't particularly like the messy way the existing cord is connected to the unused terminals on the rectifier tube socket.  I'll clean things up a bit.  Maybe get to work on it Saturday.  More to come.  Have a good one. 

Jack

[HotBluePlates]

Huh... 6SJ7.

Triode-strapped for split-load inverter duty?

[Jack_Hester]

Huh... 6SJ7.

Triode-strapped for split-load inverter duty?

I stand corrected.  6SC7 (dual triode).  I was not in my shop when I posted, and depend on a poor memory.  I went out to the shop this morning and looked.  Saturday, I will begin the process of tracing the circuit and getting it down in CAD. 

On a side note about making drawings.  I have had Visio for years, but use it only for looking at others drawings.  I recently opened some Visio drawings in LibreDraw.  I'm wondering if it has all the same functions as Visio?

Jack

[drgonzonm]

Your amp looks like a flot a tone model 500. refrigerator handle and all. Likely made in WI during the 50's.  I saw one on one of the bid sites for $200, but its condition was poor.    For info do a search for "flot a tone 500 amp"

It is considered to be a highly reliable amp.  What else do you have in your barn. 

[Jack_Hester]

Began the process of drawing a schematic, yesterday (Sat, 07May16).  I put the chassis on a small table near the computer, so that I could draw it fairly literal. 

Attached is the first draft, and I drew it the same as the tube lineup.  I will move this layout around and get it in a more conventional one.  But, this is just to get it down on a drawing. 

Both microphone cables are cut and missing.  The #2 phone jack has the ground unattached.  So, the #4 phone jack is the only functional one on the amp.  I drew the microphone jacks as I intend to connect them.  I intend to install a solder terminal strip, as well as a thermistor.  The thermistor will drop my 123vAC line voltage down to something closer to the 117vAC line that was intended.  Plus, give the amp a soft-start.  A replacement power cord (grounded) is on the bench with the amp. 

I will test all the tubes, and make a voltage chart when the amp is up and running on line voltage.  I hope to get back on it this week.  Lots of rain in the forecast, so no grass mowing to get in the way of shop time.  Have a good one. 

Jack

[Paul1453]

So you plan on using the microphone inputs too?

If you plan on using only 1 input, maybe you could reconfigure V1 to use it for 2 gain stages?

I've read that the 6SL7 has a different but very nice overdrive sound.   

[Jack_Hester]

No mods planned.  Too many years of restoring old stuff (amps, as of late) to do so.  I do, however, have some old PA amps that were trashed in some manner, that I have or will make into instrument amplifiers.  However,  if they have a schematic available, I tend to put them back as they were. 

Jack

[Jack_Hester]

Turns out that today (Sat) was the only time this week that I could get in some time on the amp. 

Replaced the power cord with a grounded one.  Installed the solder terminal strip, mounted the thermistor, and connected the power cord to it.  Cleaned up the rectifier tube socket and connected all wiring back.  Found where the original wiring was wrong, and why the power stayed on regardless of the switch position.  That works now.  Tested the tubes and brought it up again on the lamp limiter.  When I had it on full line voltage, the current draw was only a fraction over 1 amp.  Took some voltage readings: 

Line voltage:        123.3vAC
After thermistor:  120.3vAC
B+1:                   410vDC
B+2:                   337vDC
B+3:                   302vDC
V1-pins 2&5:       74.9vDC
V1-pin 3:             0.83vDC
V2-pin 2:             217.7vDC
V2-pin 5:             248.9vDC
V3-pin 3:             398.1vDC
V4-pin 3:             398.7vDC
V3/V4-pin 8:        29vDC

Forgot to record a voltage at V2-pin 6.  I'll get one the next time I have it powered up. 

Amp is dead quiet, but that may not be a good thing at this point.  As Input 3 (Instrument) is the on one connected, I plugged a cable in and touched the tip.  No sound.  Both Volume pots and the Tone pot at full.  The only time I heard a sound from the speaker is when my meter lead tip touched a tube terminal for voltage readings.  Then, I would get a pop or a hum, like I would expect. 

At this point, I'm thinking that I've got nothing coming from the front panel, and/or V1.  So, I'll stop my troubleshooting, until I can clean that up.  Depending what I find with the signal cables, I may replace all three.  But, not until I've disconnected them from the pots, so that I can ring each one out and verify each connection on the tube end.  And, record the resistance of each pot. 

Anyway, it was enjoyable getting in some shop time.  One repair that I will make towards the end is to the Flot-A-Tone badge.  Originally, it had three very small nails holding it.  The one in the middle is missing, and the badge is broken just to the right of where the nail should be.  I think I know of a means to attach the two pieces of 'pot' metal back together.  Then, I need to find a replacement for this miniature nail. 

More to come.  Have a good one. 

Jack

[Markusbwolf]

Just joined the group and I  can't believe I saw this post...two years late. I have this exact same amp, but with a slightly different panel layout. Everything else is identical; I was told it was a '54 Model 500.
My tube layout is slightly different

6SL6
?
6V6 GT
6V6 GT
5Y3

My issue is the phase inverter; I don't know what it is, but it's not a 6SC7. Right now, as of a week ago, the amp went dead, and based on most of the critical devices being replaced already; I'm suspecting this tube. While troubleshooting another issue a while back, I swapped a  6SC7 for this tube, and it stopped working. I don't have a tube tester, and haven't had time to measure voltages. I love it's tone when its working; she just needs a little more TLC.

Anyway, its cool to see another one. I live near Milwaukee, so the LoDuca family who made these, originally for accordions, are well known.
I'm seriously jealous, however...my FlotAtone nameplate is missing...I'm thinking 3D printer. ;-)

Cheers!

[terminalgs]

My issue is the phase inverter; I don't know what it is, but it's not a 6SC7.

To figure out a mystery tube, you need to start with a schematic.  flot-a-tones varied so much that even  with the handful of hand drawn schematics you'll find online,  you would need to  verify in detail that yours is a match.   you might as well draw the entire schematic.


the PI tube is probably a twin triode.  trace it back from the grids of your two power tubes.  for pins 1-8, you can figure out what is plate, grid, cathode (and heaters) by seeing what goes to ground (via resistors) and what goes to B+ (via resistors) and in the middle is the grid.


the PI is probably not a 6SC7 because that twin triode ties the cathodes together.  It *could* be, but 50s amps like the flots usually used a paraphase inverter, or maybe a concertina.   Its more likely to be a 6SN7 or 6SL7 but the only way to know for sure is draw out what your circuit is and match up likely tube basing options...