Tube amp of an old record player for guitar

[fentom_lord]

I got this old Polish record player with a tube power amp in it. I was wondering, how could it be adapted for guitar? I know I could (or perhaps I should) disconnect the record driver? What other modifications should I apply (apart from a quarter-inch input jack )?
The schematics can be found here:
http://www.mif.pg.gda.pl/homepages/tom/files/Bambino1.gif
Thanks in advance.
Matt

[Threefish]

For a while I did entertain the idea of building a small guitar amp based on one of these triode/pentode valves. If you google "ECL82 guitar", you'll find plenty of info out there from people who have. Look at their schematics and compare them to yours. You should be able to use the existing basic circuit architecture and make a few resistor and cap changes to make it more suitable for guitar use.

P1 will control volume, P2 looks like a treble cut, and P3 works a non-conventional-for-guitar-amps bass boost similar to my Goldentone Bassmaster (sort of an Aussie Bassman).

Have fun and be careful of that high voltage.

[jasperoosthoek]

I don't see why not. I built a guitar amp from a '60s reel-to-reel tape recorder and one from a radio.

It looks like your output transformer has a few taps for different speaker impedances. Does it have a selector? The speaker in the radio I used was 2.5  ohms and I had to change the output transformer altogether.

It also looks like it has some negative feedback built in. There is a connection from lug 5 from the transformer that goes to the cathode (pin 8 ) of the first triode. You can safely remove it to increase gain and distortion. Also adding a 10uF bipolar cap across the first cathode and ground (negative side to ground) will increase the gain a lot. You are going to need gain as the way it is configured right now will not be enough for guitar. It will be very clean and low output.

Have fun! (albeit in a safe way)

[petemoore]

  IEC it. Or...use an IEC cable, and fasten it.
  Clamp the ground to the chassis, first.
  Use whatever it's got that you can use, speaker ?
  There looks to be asecond transformer [probably to run the motor off of ? doesnt seem to be part of the audio circuit.

[edvard]

Nice.
I've got a 6BM8 I've been itching to wire up inside a gutted Pignose cab.
Same tube as the ECL82, different stamp.
Here's the circuit I've been eyeing, with a fistful of technical notes to get the thing humming (in a good way )

http://cool386.tripod.com/6bm8/6BM8.html

I'd love to see what you come up with.

[artifus]

http://www.radioconstructors.info/gaf2/gaf.html scroll down to aug 1962 and check out the three links to an interesting article
http://music-electronics-forum.com/t7283/ interesting safety thread

careful with live chassis - double check your wiring and have a voltage detector handy before touching anything

having said that i've done this with three units prior to finding the above info and didn't kill myself despite being young and stupid, but maybe i'm just lucky. just jack to pick up input. one unit has an all in one transformer/motor assembly so the motor is always running. the article linked to above explains i think, i haven't read it in a while. i keep meaning to fit a disc with holes in it or something to the spindle and a led or lamp for some kind of optical trem but haven't got round to trying it out yet - it'd be a fixed furious speed anyway. hmmm, may have to go dig out and revisit some old boxes...

[fentom_lord]

Hey,
Thanks a lot for all the suggestions. I sure will study the info you people have provided and mess around with this thingy a little bit
As for safety, I do realize there are lethal voltages in tube circuits, so I will approach it with extreme caution.
There's one more thing I'd like to ask about, if I clamp the ground to the chassis and everything's wired correctly, a voltage detector should indicate NO voltage on the chassis, right?
Thanks.

[Brossman]

@artifus -- could you not rig up a control mechanism (pot?) to control the rpms of the motor?  If the motor runs at all, it is likely that there was a way to switch between record speeds (33.3/45/78)... and if so, you could use a pot to more precisely control the speed instead of switching between presets.

Then again, I don't exactly know how to do this, as I'm an electronics noob.  **lightbulb** at my job, we have speed control boxes for motors that drive a belt system (sounds like a turntable motor! )

[petemoore]

  Some are wired 'funny' for PS input.
  I had one with the motor winding as part of the PS for the record player.
  Noisy motor was about 1/2 as loud as the amp, so conversion to safe guitar amp would require a Power Transformer to convert input supply voltage..and..allow for safety ground.
  I was tempted to go into more details...without PT, you need PT to make safety ground. I don't wanna typo a power supply instruction, so 'just know' somehow, there are good sources ont he net for.
  AC comes in USA through the two identical or nearly identical prongs [nearly identical I / C prongs...one is wider and so the plug only  goes in the wall one way]. Hook this up to the PT, AC has no polarity...and the amp'll work.
  But the chassis is whatever voltage it decides it wants to be without a ground wire clamped to it, this is not good for Hum or other equipment , including humans.
  I skipped over that amp, it worked but...loud phono-motor and hum and...unsafe. I found other stuff with suitable PT...more inviting. 
  IEC plugs are cheap, and wiring one up is ~easy, mounting it is relatively difficult, for rectangular holes in [not too thick] metals I start with rectangular drill template at the corners of the rectangle-hole. Then I use big pair of heavy duty wire cutters...nibbling to start the tear between holes [from both of two holes at the end of a striaght line], once I nibble through one or two of the 'jigsaw' type cuts [using wire cutters, nibbling with just the tip, but rotating the cutter tool also, just not enough to distort the outside of the cut-line.
  Then tearing can begin, starting with the heating of the cut-line [back and forth with the...whatever tool grabs the tab you wanna remove [plier ?].
  Fix up the edges with a file.
  There's a nibbler tool also./0

[edvard]

...
i keep meaning to fit a disc with holes in it or something to the spindle and a led or lamp for some kind of optical trem but haven't got round to trying it out yet - it'd be a fixed furious speed anyway. hmmm, may have to go dig out and revisit some old boxes...

What an AWESOME idea!
Ok, clear plastic disk, LED on one side, LDR on the other, black spray paint blobs, stripes, lines, etc for any number of funky trem patterns, kinda like an optical Optigan.
Or, old record you will NEVER want to hear again, drill holes at regular intervals around the rim, about a half or quarter inch away from the edge for a more "choppy" tremolo.

The possibilities... wow...

[petemoore]

 i keep meaning to fit a disc with holes in it or something to the spindle and a led or lamp for some kind of optical trem but haven't got round to trying it out yet - it'd be a fixed furious speed anyway.
  You can fit platters with differing frequencies of light holes, or 1  record sized platter [with holes or slots, shapes in it] with various patterns of holes for each 'song'...slide the LeD LDR arrangment in and out like the record needle, you can probably fit four or five 'tremolo frequency song patterns' on each disc.
 It'd be so much easier to stamp the platter [plastic record platter], and would require a lot of drilling, intuitive hole template pre-design [or get rid of all but enough of the platter surface to make an easier to shape light blocking substrate on that, just leave enough platter surface metal so you don't bend it.
 Since you have PS, something very bright on the other side of the LDR/platter should be easy to cobble in and allow low enough R-bright even with the LDR/LED separated by an inch or so.
 A disc section with 2 holes of course would be 1/2 the frequency of modulation as on with 4 light-holes, of course off-balance and non-linear...nmore random types of trem modulations could be cut in to the record.
 say 1 revolution = 1 - 10
 1    5     10
 1  3   6   10
 12        7 10
 12   45   78  10
 As the disc spins and the LDR/LDR looks through what amounts to player piano songsheets you cut out and place on platter.  
 Swapping platter patterns or turning knobs: pulse width, and ramp rates can be controlled.
 Swapping patterns of course is 'switching' not analog control...not bad because you can Needle-Slide the LDR.
 Except for the drilling/cutting of the platter, not too tough...put some foam behind the needle, set the height using block or some phonographs had 'lift' adjustment even, ride the needle down he rail. Use rubber band or something to keep it pinned where you want it. Use light strip across the player portion of the platter.
 I'm not looking at the record player, A miniature version DC motor thing worked for AF1 returned a very aggressive ''rightsplan'' to me with this one, IRC...lol !
 Have fun with it !
  Then if you feel real fancy and get bored with that, rig up an envelop control for the light circuit, or across the LDR..such as a light for attacks that shines on the LDR.

[Jazznoise]

Well there is the issue, depending on the age of this, of the RIAA EQ curve or a similar curve. Records need to have alot of high frequencies pumped into them before cutting for them to actualy get picked up by the needle, of course since no one wants all this harsh treble there's an EQ built into the record player that does the opposite and cuts the high frequencies! But, then, maybe that'll sound good so experiment with your RC values.

http://en.wikipedia.org/wiki/RIAA_equalization - Lots more information

As for the tremolo idea, not only is it a good idea it'd be great! You could have a disc with alot of holes and it'd go into the audio frequency - you'd probably produce ring modulation!

[jasperoosthoek]

@Jazznoise

I knew that and I checked the schematic for evidence. There is no RIAA EQ going on as this is only the power amp. The equalization is as far as I know always done in the (first) preamp. This thing has two tubes and will make records whisper when maxed out.

[petemoore]

  Probably intended to run 'the' speaker at least.
  so many watts. Boost the input.
  Yea, The LP-Tremolo would look too cool, spinning circle of light holes.
  If you'll be draggin' that platter around anyway, why not put it to some use?

[artifus]

thanks for the opto-disc ideas, plenty to try out when i eventually get around to housing that project. back on the safety vibe for mo, i just bumped into this: http://www.instructables.com/id/Isolation-transformer-upgrade-for-old-guitar-amps/ which some may find useful.

thinking again about the opto-disc non-linear analogue 'progammable' (by changing disc) tremolo... would a smaller battery operated stompbox version be worth playing with - salvage ir parts from old pc mouse, small dc motor from game controller/whatever with pwm speed control? just thinking out loud...

[petemoore]

thinking again about the opto-disc non-linear analogue 'progammable' (by changing disc) tremolo... would a smaller battery operated stompbox version be worth playing with - salvage ir parts from old pc mouse, small dc motor from game controller/whatever with pwm speed control? just thinking out loud...
  It is possible to have a rotating disc and related motor powersuply boxed aside one another, if designed well, without noise introduction.
  I'd study and then consider use of DC motor and consideration to noise relationship of motor PS near small signal amp.
  As well as speed control.
  An up/Down barrel type song-shifter is option which reduces the gearing a bit, tightens build precision requirement and footprint. Somehow the led/ldr wiring goes through the rotating shaft [hard] or around the corner of the rotating punchout sheet [easier..
  Find something that already goes slow, steady and quiet enough...

[PRR]

> Records need to have alot of high frequencies pumped into them before cutting

No.

Records are cut nearly constant displacement.

90% of the "RIAA curve" is about the PICKUP. It is specified for magnetic pickup. This is a velocity sensor. For constant displacement, the output RISES as frequency rises. The preamps's first job is to apply an opposite drop.

For mostly-historic reasons, RIAA has a wiggle at 500Hz and 2KHz.

Now, most low-cost players including this one used crystal pickups. Output is proportional to displacement. The record plays nearly flat without massive EQ. There is the 500Hz-2KHz jog; most cheap players simply used a bright speaker and let it go at that.

The Bambino plan shows 0.1V input for 53V at final plate. I think the full-roar level at final plate is more like 150V, so you need 0.3V at input for maximum scream. Guitar amps are usually scaled for 0.02V input makes maximum output.

You can find a little more gain by dinking with the NFB loop from speaker back to first cathode. But I suspect there isn't much gain to spare, not enuff for a responsive gitar amp.

You want another gain of 15 in front of this.

You could wire-up another tube. It will probably stand the load of another heater, especially a single triode (typically a triode-diode).

It might be easier and cooler to stick a JFET or MOSFET booster in front.

For power: note that the output stage cathode sits near +15V. Increase its cathode capacitor to maybe 220uFd 25V. Tap this point to power a booster.

After that: it should be as good a guitar amp as it was as a record player. (And it is clearly a very low-cost un-fancy record player, what we used to call junk.) About 2/3rd the power of a Champ or EPI Valve Jr, but the speaker is less than you'd typically use on guitar amp. (Try it into a Full Stack... it may be interesting.)

> I could (or perhaps I should) disconnect the record driver?

The motor? Why? Are you afraid it will be worn-out before you play a record again? No, the oil will gum-up and the rubber wheel will dent and lump, but the motor will keep trying to work.

Sound may be better if you snip the wires and lift the whole mechanism out, cover the hole.

> could you not rig up a control mechanism (pot?) to control the rpms of the motor?

No. Or no simple way.

The motor turns at power line frequency, 3,000RPM in Poland. There is a 3-diameter stepped shaft on the motor. The speed selector puts the rubber wheel on one of these steps. Yes, you can take the shaft out and turn it on a lathe to a taper, modify the speed selector for infinite motion instead of 3-step selection.... awful lot of work. You could instead build a 40Hz-90Hz oscillator and a 5 Watt 230 Volt power amplifier to feed the motor "fake wall power" with a limited range of speed. I have done this for a special project. It's tricky, and the motor does NOT like to be pushed too far.

[fentom_lord]

Hey there,
After many days of not having the time (and being somewhat afraid too), I finally got round to messing around with this record player. So far I managed to put a .25" input jack socket and plugged my guitar into it. Hey! It didn't explode and sounded nice. What's more, my Digitech Metal Master pedal sounded quite decent too.
I'll try to record a few samples and post them somewhere.
Matt

[jasperoosthoek]

Good work! Like to hear the samples  .