Scored a Kalart Victor Projector Amp

[Platefire]

I went Flea Market/thrift shop hopping today and picked up a Kalart Victor Projector for $10 that has a tube audio amp in it. Now that I got it home I find the tube configuration 7025 preamp, 12ax7 pi, two 6973 power tubes and a 5Y3 rectifier. The 6973 power tube is a new one on me?? I looked it over a little but have no idea how it will go separating the audio amp from projector. Tried to find a schematic but so far no go. Here is some pics. Platefire


BTY-Other things picked up on todays run+Rocktron Short Timer Delay $25 and Poland Wild Thang Chain Saw with 18" bar $60

[2deaf]

I just completely rebuilt a Univox with 6973's and they sound pretty cool when overdriven.  I used EH 6973's from AES.  The things have a maximum plate voltage of 440V.  I have them running with 393V on the plates and 291V on the screens with a Heyboer 18W OT with an eight thousand something primary.  Just about straight out of the spec. sheet and they seem to like it.   

[Platefire]

Kinda sounds like a 6973 is a little more than a EL84 but less than a 6L6😋

[eleventeen]

Nice score, Plate! 6973 is a perfectly respectable tube, more or less equal to a 6V6. 


http://www.enjoythemusic.com/magazine/manufacture/1108/ (prose comparison among several tube types)

[PRR]

> 6973 power tube is a

6V6 with a 440V rating, 500K Rg in fix-bias.

Rare, getting expensive NOS. E-H has a "equivalent".

Your "15 WATT" is likely running 300V B+. In a bind, punch for 6V6, or wire for EL84 and change bias.

[kagliostro]

Oh la là

Nice Score


Franco

[eleventeen]

PRR, you seem to be implying that 6V6 is a cheap tube. Nope, not any more. I don't see them selling for under $20 any more. Most likely a 6973 would be (only) a buck or two more. Just sayin'.

[Platefire]

Thanks! I like the idea of rewiring/re-biasing for EL84's---I've got a truck load of those:>)

But those 6973's are vintage RCA's and the preamps are RCA blackplates--so it might be interesting to see how they all work first. I did fire up the audio amp briefly and it did work in its existing state. The audio amp is so buried up in the projector housing I can't tell much about the chassis configuration. I can tell that the on/off vol and tone control is in a different place than the main audio amp chassis--so no telling what kind of crazy configuration I got??

First chance I get, I will peel the projector parts away to see what my audio amp situation is----the issue always is---is there room to mount a fuse holder, power cord, input jack, Pilot light, vol, tone in the existing amp chassis so it can be operated as a separate independent amp apart from the projector. Platefire

BTW-Finding something like this always reminds me when I first started into amp building/conversions and I was always on the hunt:>) I still do, just not as intense!

[kagliostro]

If you peel the projector parts away I would like to see a pair of photo of the amp (if you can)

Franco

[Platefire]

Well it has been raining this afternoon so I thought it was a good time to
to open up the projector and see what I got. I must say for any amp possibilities from existing is pretty disappointing. No easy way to make it into something from what's there. I guess I got some good parts for the money. As you can see the main board with traces. Oh well, I'll think it over. Any Ideas? Platefire

[sluckey]

Oh well, I'll think it over. Any Ideas? Platefire

Yeah. Get back on that plexi project! I ain't gonna live forever and I'd like to see the finished conversion.

[eleventeen]

Looks kinda like it would more trouble to try to adapt it than to gut it and throw the parts into an 18 watt Stout (or some other) chassis that you buy and take delivery of in a box with all the holes drilled.

[Platefire]

Yeah, your both right. Transformers and tubes for a latter project. I'll not waste any
time on this but get back to the Hot Shot 48😉 Platefire

[kagliostro]

I'll be not so sure about to abandon the amp use and go for parts supply

My consideration starts thinking to use the amp with those power tubes that you say are still working

remember you can get new ones for 22$ each, not an impossible price

http://www.thetubestore.com/Tubes/Electro-Harmonix/Electro-Harmonix-6973

So, to me, the first thing will be to trace a schematic and only after that decide if a guitar adaptation is feasible

Franco

[eleventeen]

Franco, we are saying that the physical build of the 6973 projector amp is so strange that to put it in a box that looks like an amp would involve a lot of work. Plus it is built on a PC board, and while some of us have a fair amount of experience with PC-board builds and modifying them, I don't think Plate likes them much. I am just saying, to my eye, I could definitely see re-using the PC board and modifying it to be a guitar amp (not really very hard *IF* you have the experience doing so) but if one starts the process in a more standard chassis, it would be much easier and the end result would be more usable. To my eye, it is much more a mechanical problem-child than an electronic one.

[kagliostro]

.... is much more a mechanical problem-child .....

Oh, yes, I see ..... the mechanical problems are those that I feel more confident to solve, so often I don't remember that for someone they can be difficult to approach


Franco

[PRR]

> to put it in a box that looks like an amp

So don't make it "look like an amp". Take out the heavy mechanicals, extend the "phono" jack, use the internal speaker until it dies. It's not much more than a practice amp, but if you do gig out with it, you can be sure you'll be the only Kalart-Victor player on the bandstand.

With the clockworks out, you have space for several pedals or several pounds of oregano.

BTW: http://www.acofs.org.au/part_5_files/Kalart/Tech%20KALART%2070%2015,25.PDF page 33-46  This is 70-series, yours is 75-series, but the differences may be small.

[PRR]

http://www.acofs.org.au/part_4_files/Kalart/Kalart-general.htm
"The valve amplifier delivers a soft, easy-to-listen-to sound"

Kalart was a well-known name in press cameras; nearly every Graphic/Graflex sported a Kalart rangefinder. They also did movie sync and flash for focal plane shutters.
https://lommen9.home.xs4all.nl/kalartmain/index.htm

[Platefire]

Wow!! Thanks much PRR! I downloaded the 70 manual. It had schematic and board layout drawings for the 70-25 Amp(25 watts) and the 70-15 Amp (15 Watts) the 70-15 looks like the same amp I got in my model 75 if not identical. I haven't weighed it but my goodness, the thing must weigh 50 pounds or more! Very well built.

The other night when I removed the projector it had a RCA cable going from the projector head to a RCA jack in the amp. I think that was the main audio feed from the the projector tape heads. Well I unplugged it when I removed the projector.  I had a 1/4" to RCA male converter and plugged that in the amp RCA input, then plugged my guitar into that. I fired the amp up with existing speaker---it worked! The amp was really quiet running, the sound was very clean even at full amp volume. The tone stack seem to work ok for guitar. The drawback was for two PP 6973's it didn't get very loud at all--no distortion---but off course the circuit is geared for clear mellow audio to go with a picture.

Now that I got a schematic, I can at least scheme on how I might convert to guitar. Something to ponder on a rainy night. So kagliostro I've conquered more severely difficult mechanical/physical amp projects than you arn't probably aware of. This one is not impossible but has got it's difficulties. I will let life issues dictate rather I spend time working this puzzle out. Old men in my situation have their priorities:>) As the disappointment of this find being such difficult amp project wears off maybe I can get shifted into a new perspective on it---but the Hot Shot 48 comes first. Platefire

BTW-I don't find a normal amp fuse on the amp but it does have a reset button that looks like it tied to the power cord AC. I'm assuming this is like a circuit breaker, if it throws you just reset it???

[eleventeen]

There *might* be a wired (between two lugs on a terminal strip) fuse inside the amp. This is a projector that probably used a 1200 watt (10 amps AC consumption) bulb and it was certainly possible to run the amp inside the projector WITHOUT using the bulb, IOW, just as a PA or record player amp. So a mild overload in what you might think of as a 5E3 Deluxe is not going to trigger a (probably) 15 amp ckt breaker unless you have a blazing catastrophe.


You're also going to get a mildly distorted view of what the amp can do running that 6 x 9 speaker. Got an external cab? I still would not expect it to break up like a Tweedybird.

[PRR]

> a RCA cable going from the projector head to a RCA jack in the amp.

ACK!! Don't even touch that!!

Use the Phono input!! That's what it is for!!

(Old-time phono pickups were a lot like guitar pickups, only higher output because they shook mechanically, not sensing a string at a distance. Newer phono would be high output ceramic. You probably want a boost pedal.)

The _film_ sound head, on most 16mm, was NOT "tape" but optical. And the electric eye which sensed the optical sound track needed high voltage!! Low current, "may" not blow up your guitar or drop you to the floor, but sure not nice.

Sorry for not emphasizing this point.

At a glance, I think the 70 has 3-screw cover over PCB and the 75 has two 2-screw covers. And several feature-levels of each series (w/mike, 15/25W, etc). I'm sure the 70 manual gets you where you need to go.

[Platefire]

OK PRR, maybe you can help me out further on this. I did try the phono jack first and got nothing, that's why I tired the other input and did get something on that.

But if you have time go to the manual---I'm looking at drawing #47821-1. For your information, the components numbers identified in a circle are p to p and the ones in a square are on the board. In the upper left hand corner of subject drawing it shows the two inputs. Now on my amp the one that works is a RCA female and the Phono is a 1/4" jack. The #1 in a circle futurist to the left shows the input going to a tube identified in a circle #72 identified on the material list of this drawing as NUVISTOR-JIB??? don't sound like a tube but looks like one on the schematic. I didn't see another tube when looking at the amp other than what is shown on the tube layout. I was thinking maybe if the tube/component is bad, maybe that's why the phono input didn't work??? It appears to be an extra gain stage for the phono jack that goes through 500K vol pot(#19) to input pf the 7025 tube(#41).
Or either this schematic is not a perfect match for the model 75-15? Platefire

[kagliostro]

The 70 15 schematics (from the pdf manual)







Franco

[PRR]

> NUVISTOR-JIB??? don't sound like a tube but looks like one on the schematic.

Google is your friend.

A Nuvistor looks like a huge transistor.
http://www.r-type.org/articles/art-150.htm
The socket (assuming the Nuvistor may be missing) looks like a big old transistor socket.
http://www.r-type.org/articles/art150e.jpg

[PRR]

A Nuvistor IS a tube. But small and metal. Maybe you could read the links?

But look. Find the back of the RCA jack. There is a 0.005u cap and a 10Meg resistor in the jack tip contact. Snip the jack end of the 10Meg. If possible, re-solder it to jack shell or chassis ground. The 80V feed to the electric eye, through 10Meg, is a very small safe current, but something you will never need or want again. Throwing that feed to ground leaves no live wire in that area and doesn't disturb the rest of the B+ enough to matter.

[sluckey]

A nuvistor is a tube! Although it is tiny. Some don't even have sockets, just wires coming out of the glass.

[Platefire]

Thanks! Yes I took a look at the links. Very interesting. Those came out right at the end of the tube era and beginning of the transistor. Ha, apparently my NUVISTOR failed--but that's just an assumption at this point. If it has pins--may have lost connection.

When I get a chance, I need to remove the "L" chassis out of the case in able to get a better look at things and see about 10Meg and that 80V feed. When I was playing my guitar through that jack I was getting a popping static when I flipped my pickup switch and turned the volume knob---I was thinking some DC was leaking into the grid---might of been that 80V?

Thanks kagliostro for posting the schematics!!!

Platefire
 

[Platefire]

OK Guys, cats out of the bag! No NuVistor that I can find. I've took some
New pictures, so see if you see anything that looks like it. From what I'm
Seeing the correct schematic should be 47821 instead of 47821-1.

As I look at this I'm thinking kind of the same thing PRR suggested in modifying existing
For guitar using the same case---a re-purposing. Could install a 1/4 speaker jack to hook it up to other cabs. I checked the Ohms on the existing speaker and it measure 9 Ohms---says 8 Ohms for in Item #59--so that would match my other cab Ohms. I still can't understand why the phono jack didn't Work because that's perfect for guitar input. I did a continuity check on that jack and got a beep up to the 1.5 meg R on the board and a beep from the 1.5 meg to the 27K R grid stopper tied to 7025 pin 7-----so that pin 7 worked with the RCA, why not with the 1/4 phono? Haven't disconnected the 15 meg yet but will before I fire it up again. I would like to give the Phono 1/4 Jack another go to see if I can get it working. Platefire

[Platefire]

Pics continued

[kagliostro]

No .... I don't see nuvistors there 

---

Looking to the nude amp seems it will be easy also to give it a combo style cab, only the faceplate will be on the left of the front panel

instead that in more usual positions (if you decide to have a wood cabinet (with one other speaker ?))

The more I look to it the more I think it was a nice score

Franco

[Platefire]

Yeah, I was just thinking if you put it in a cab like you say that would have a control panel like a silvertone 1482:>}

Well I experimented a little. I clipped the 10 Meg resistor power supply to RCA. Not enough lead to tie it to anything, so I left it hanging in the air.

I tried the phono jack this time and it worked! But volume same as RCA. I put an alligator clip jumper over the 1.5M grid resistor on the phono jack and the gain jumped up some. I was thinking of putting another jumper over the tone stack to see what that did but didn't. I'm sure there is a lot of this circuit you can remove or change to get the gain up. I think the first step is to remove the 1.5 Meg part # 13 and install a permanent jumper on the board. Think the existing 27K grid stopper on pin 7 is fine. Platefire

[kagliostro]

Silvertone 1482  ..... yes, that is what I was meaning

---

Don't need to be cut off the Tone Control, the circuit has 3 triode before the PI (2 x 7025 - 1 x 12ax7) working around plate and cathode

resistor you'll obtain what you are looking for

EDIT:
effectively there is something that seems require to be revised (so seems to me) the circuit around TS and V1b is odd to me 

Franco

[sluckey]

effectively there is something that seems require to be revised (so seems to me) the circuit around TS and V1b is odd to me

Do you mean the feedback circuit from the plate back to the tone network via that red shielded cable? The real baxandall circuit is a feedback type tone network. The tonestack that we sometimes call baxandall and usually see in guitar amps is really a James tone circuit and has no feedback.

[kagliostro]

Yes Steve, thanks

the red shielded cable is what was odd to me

unfortunately I remembered, and remember, only passive baxandall (and James), but no "active" baxandall

I think Platefire can modify the Tone Control in a James and use V1b as a gain stage (if he want a high gain preamp)

Franco


p.s.: A more readable schematic about active baxandall

[Platefire]

Har! I'm at Wally World Looking at this sitting on the bench by the door.

On the tone stack on the schematic there is an area marked by a dotted
Lines that's a rectangle. Everything inside that dotted rectangle is in
A single component that looks like a large rectangular ceramic disk with many leads that
Is wired to the double tone stack pot. So with that you either have to use
It or do a complete rewire when removed. Trouble is finding space for a rewire
With full size components. Just saying in case you didn't know?

I checked voltages with the schematic and everything is reading about 7VDC
over that is pretty normal for vintage stuff. Platefire

[PRR]

> get the gain up.

Someone check my math. I figure the input sensitivity for full output is 16mV. 20mV is a fine sensitivity typical of classic Fenders, so you shouldn't be short of gain.

Another rule of thumb: two 12AX7 gain stages (not counting unity-gain tone or inverter stages) will get from guitar to 6V6 just fine. You got that.

How much tender loving preventative maintenance has this amplifier had recently? The last time I saw a 16mm projector *run* was when the porn-theater was being torn down in the 1980s. (And those flix were silent.) I'm shocked it isn't a hum-bomb. I'd still suspect every electrolytic in the signal path, which isn't much. Also the tubes (though good volts on 12AX7 suggests the little bottles can't be too sick).

[PRR]

> no "active" baxandall

Baxandall published THE most well-known boost/cut bass/treble Negative Feedback ("active") tone control circuit. It was famous when published, though wide use came later (with stereo).

James published a survey of tone controls and a plan with values for a passive boost/cut bass/treble tone control circuit. The paper was less known but somehow everybody knew the circuit.

The Bax with tube is unity-gain.

The James has "gain" of 10/1, a strong loss. Yes, if you add a tube the net gain may be near 5. In hi-fi this gain adds enough distortion to look bad on the specs, so the tone-recovery stage would have NFB to reduce distortion, and gain comes out about the same. Guitars tolerate or improve with a little distortion.

For "flat when centered" knob action, the Bax uses Linear pots, the James must have 10% taper pots. While appropriate mono pots were available, tracking two taper pots is more difficult in Stereo, which is when the Bax became common.

The different tapers is why it does not make sense to "convert". If it was two holes for two pots, OK. But it is one hole and the chassis does not invite more holes unless you are really going to CHANGE it.

[Platefire]

Well I tell you what PRR, there are no flies on the existing tone stack. I got home from Wally World tonight and tried a few things. First I got out my DeoxIT and cleaned tube pins, straightened with my pin straightener, cleaned the pots on vol and tone stacks. I also remove that 1.5 Meg grid resistor in the phono input off the board and soldered in a permanent jumper. Last thing I did was create a special cord that would plug in the existing speaker out and plug into my 1-10 DIY cab with a Eminence Ragun Cajun Speaker. I also pulled out my 80's DOD Analog delay.

Results, quite a boost in the volume. I would say the volume in loudness probably comes close to rivaling my Silvertone 1482 but with better clean headroom. The clean tone and headroom is very surprising in a good way. Nice clean tone and the tone stack is allowing me me to get a good thick tone like I like with still some nice highs in there too. The response is touch sensitive and not stiff kind of like a good fender. I tried a strat and a humbucker PRS copy and both of them felt very good & Sounded good through it. The better quality speaker made a huge difference. So my analysis at this point is:

1-Happy with the sound and response. The tone stack is set pretty much in the middle slightly boosted treble and bass at about 1:00 oclock. It's a good sign that I'm not having to go to extremes settings on the stack to get what I need and have additional room to dial more lows or highs. 

2-Would be nice it it would get a hair louder. I have been running the vol at about 75% which is kind of high from my norm and the operating noise is not to bad but when I get up close to full vol the noise is kind of loud. My norm is from 33% to 50% vol. May be those old filter caps causing the noise but just about any of my amps get noisy around 75% to 100% vol---so that is why I say it would seem more normal to get the volume I'm getting now at 30 to 50% vol instead of 75% vol based on my experience with other PP 6V6 Amps I got.

3-The existing tubes seem to be doing very good at this point. All vintage RCAs. I think a PRR said, are pretty healthy. Seems like the old thang is doing pretty good. I'll get back to testing:>) Platefire     

[kagliostro]

Ottimo 

I was already thinking of suggesting to move the volume potentiometer in place of that of the tone control in order to then make another hole

next to the one where was the volume and have two separate potentiometers so you can change the existing control tones

but it seems that it does not make sense, since you're happy with the circuit as it is now

Franco

[PRR]

> 75% which is kind of high from my norm

It's not a guitar amp. Don't expect the knob marks to be the same. Guitar amps may be calibrated to get loud "quick" to impress the buyer. Movie amps may be calibrated for a long "medium" zone to be easier to set for passive audience. Set it for happy sound.

The original speaker is of course puny; also there are clues it is mis-matched to the amplifier. Additional speakers would be used for large venues. Aim around 4 Ohms, and as in all "loud" guitar work, big light cones are best. The 6x9 may still be a fine patio player.

[Platefire]

Well I guess the amp is loud enough. I was Jamming with my JamMan
Backing tracks over my PA and the wife came bursting
Into the room demanding I turn down----so I guess it passed
the "Please Turn Down" test. It's still sounding very good! Platefire

[kagliostro]

If, one day, you put it in a wood cabinet I would like to see it


Ciao


Franco

[shooter]

it passed the "Please Turn Down" test.

I was whaling on my last build, nobody home, when I started hearing small arms fire every time I cranked on it, dialed it down, gun-fire stopped   Gotta love the country life!

[Platefire]

PRR, did I understand you to say my Baxandall is active? If so, what makes it active?

I've been looking V1b and the two connections to the tone stack and is that the negative feedback circuit---signal from V1b plate fed through the .005 cap back to the tone stack and routed back to V1B grid??? Not familiar with this, so I'm trying to get a general understanding of it.

Also on the schematic when you put the figures saying, check my math. I have no idea what that is?

Another thing I was wondering about is what is all that circuitry attached to the PI cathode. Looks like a lot going on there, maybe a feedback circuit from the cathode back to grid and also just before the input grid on the power tube. Some things I'm not familiar with?

Also can anybody tell from the schematic what the transformer speaker tap ohms is. I know the speaker that came with it is 8 Ohms. All I seen is on the OT green tap is a note "DC resistance .19 Ohms" ---don't get that. Any help appreciated:>) Platefire

[kagliostro]

This is the Cathodyne PI on Merlin's pages





and this is the PI of your amp




What do you see of odd ?

Do you see other parts that I didn't recognized ??

EDIT:

Do you mean the voltage across resistor #22 ?

Franco

[Platefire]

Well I thought something strange was going on with the bottom 6973 on the
Schematic
With the grid but upon a closer look it appears everything is pretty normal.
Thanks for the nice illustrations, looks like nothing amiss here. As ZZ Top
said on one of his songs "I think I may be mistaken"😉

One thing I would like explained to me is on the output of the tone stack?
Why is the plate output of V1b through #5 .005 capacitor tied back into
The tone stack ------it that a NFB feed back to tone stack or what is it's
Purpose? Platefire

[kagliostro]

I'm not able to explain you how it works in details



but that Tone Control is active and has NFB

here is an explanation (scroll down till you see the Baxandall)

http://www.ozvalveamps.org/tonestacks.htm

Franco

[Platefire]

Thanks, I checked it out. Looking at the boost/cut directions
on the schematic it appears that clockwise movement is cut and counter clockwise
Is boost. Is That the way it works because I was thinking boost was clockwise? Platefire

[sluckey]

Looking at the boost/cut directions on the schematic it appears that clockwise movement is cut and counter clockwise is boost.

There's no way to tell which way is CW or CCW from that schematic. An arrow pointing to the left is not necessarily CCW.

[Platefire]

OK, thanks! My boost is definitely clockwise. The gain of the amp stays pretty consistent throughout
The  movement of the stack. Platefire