seeburg amp question

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paulrevelcet
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seeburg amp question

Post by paulrevelcet » Wed Oct 06, 2004 4:42 pm

Hi all, I recently finished up my jukebox project, or at least I thought I had, everything works great except the volume is not very loud, like 75% less than one that a restaurant has down the road, question is where do I start in tracing down the problem, its a type SHFA1, any help would be greatly appreciated.

Mike
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Re: seeburg amp question

Post by Mike » Wed Oct 06, 2004 5:46 pm

How bout building a nice new amp for it?<p>a gainclone based on the 3875 or the 3886 would be a great choice, for 56-70W depending on the chip.

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Re: seeburg amp question

Post by paulrevelcet » Wed Oct 06, 2004 9:02 pm

I dont feel it would be a restoration, I started the project to learn about tube amps but more than that, to thumb my nose at the disposable that I have grown to despise, and Ive gained a whole new respect for mechanical engineering, beautiful bit of enginering ,those old jukeboxes, all those moving parts and lots of them are still playing records just as well today as they did 40 years ago, and yet my solid state T.V. that I bought about 3 years no longer works, there is a poetic statement somewhere in there I think, but all I can manage is *&*+$#$.

Enzo
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Re: seeburg amp question

Post by Enzo » Wed Oct 06, 2004 9:13 pm

Where's the challenge in that? You not only have to make it fit, but it has to mute and do other things, and then there is the matter of power supply. Wait, I guess that is a challenge.<p>The SHFA1 has several places to get back gain. Is this the one we discussed a little while back? With the transistors?<p>Does the restaurant have exactly this model? Or just something that looks similar? Does it have the stock amplifier in it?<p>The two channels are good for up to 20 watts each. Make sure the speaker switch on the amp is set for the most power - I think it has like 1-2-4-8-16 watt settings or something like that. Max it.<p>Remove the two 6BJ6s - the tubes furthest from the transformers. They are the AVC tubes and they sap gain. In fact I go a step further and remove the tubes and the caps they use as well- C108, C147<p>6973s are not cheap, but they may be weak, along with any other tubes in there.<p>Do you have the schemaric so I can refer to parts?<p>Did you look for leaky interstage caps? These amps are typically full of them at this age. The output tube grids should have about -35 volts on them. A leaky interstage cap there will fight that bias voltage with positive DC from the previous plates. If that -35 is low or even positive, your caps are bad.<p>Some guys just replace all the caps. I tend to check each one. This amp may well need a dozen film caps per channel.<p>Are yout speakers original? The juke speakers were very efficient models. SOme aftermarket or RadioShack speaker may be far less efficient. Remember that twice or half power is a 3db difference. Other side of that coin is that a speaker that is 3db les efficient will sound the same loudness as the original running on half power.

paulrevelcet
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Re: seeburg amp question

Post by paulrevelcet » Thu Oct 07, 2004 4:16 am

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Does the restaurant have exactly this model <hr></blockquote>Yes. <p> <blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Does it have the stock amplifier in it? <hr></blockquote>Yes.<p> <blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Is this the one we discussed a little while back<hr></blockquote>Yes.<p> <blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr> Do you have the schemaric so I can refer to parts <hr></blockquote>Yes.<p>All ready removed the two 6BJ6s <p>All tubes are new, All caps are new, stock speakers, the amp sounds great, just to low, you could talk over it in a normal conversation, standing beside it. I have thr original service manual for this jukebox.

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Re: seeburg amp question

Post by toejam » Thu Oct 07, 2004 5:16 am

ont thing you can check is the needle seated completly in the cartridge?
Did you try to play it before you recapped it?
I'm not sure if thoes models had a motorized volume control if not, check the connections to it with the schematic and ohm out the pot.
Make sure there are no jumpers missing.
Check out the mute circut.
With the amp on grab a rag and wiggle out the phase invertor tube if the static is louder than the music, go back one tube and do the same thing you can sometimes localize the problem that way.
good luck
tj

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Bob Scott
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Re: seeburg amp question

Post by Bob Scott » Thu Oct 07, 2004 10:14 am

You might also check the ceramic or crystal cartridge. When I was about 12, we had one that needed a lot of amplification, and the sound was a bit distorted. Turns out the crystal was cracked.<p>Bob
-=VA7KOR=- My solar system includes Pluto.

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ModRob
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Re: seeburg amp question

Post by ModRob » Thu Oct 07, 2004 1:04 pm

Another very interesting post from you guys...<p>I have a Seeburg 1963 LP1 that I brought back from the dead. I did alright, except it plays all 45's on the A side, but won't play B sides...lol...my next project will be putting new parts in the amp. Right now, it's biggest problem is that when first turned on, the volume is moderate, but grows louder as it plays. After about 30 minutes, it gets much better....<p>After all the troule I've caused myself with this danged Ms. PacMan game, I might be better off to leave my juke alone....lol.

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Edd
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Re: seeburg amp question

Post by Edd » Thu Oct 07, 2004 2:26 pm

SEEBURGER_POST_INFO:<p>Now, wouldn’t that be just about ’59-60 vintage on your mean music machine?<p>On evaluating the tubed power output stages, a simple procedure would be to take a shielded line with an RCA male on one end and have the lines other end retain its shielding , up to about an inch from its end and connect a short leaded approx..01-.1 ufd paper/poly/or/ceramic isolation/coupling capacitor and (with a ground lead to the shield wire) and then connect that ground to the amp common and use the cap to inject a test audio signal in to pin7 of either of V110/V104….12AX7 power amp preamps for your AF power amp. Your audio test signal being derived from a playing CD audio player. That level should drive the power amp solidly using that injection point, however, to inject into earlier staging would definitely require an attenuating down of that audio level.
The most troublesome points in the tube power amp proper would be coupling caps C133/C172 into their V104/12AX7 and V110/12AX7. Then C137/C175 into their V105/6973 and V111/6973 along with C138/C176 into their V106/6973 and V111/6973’s. The most discriminating test of any leakage at all is to just leave the cap connected to the plate end of its connection and unsolder and float the other lead and then power up the amp and connect to the floating lead and monitor for voltage …AFTER a wait for the initial startup charge to diminish downwards…after that then if there is any static voltage being monitored at all…replace that cap. An ohmmeter testing is in no way as subjective as this dynamic mode of testing. A high Z metering is also preferable…such as would be presented by a Digital voltmeter/TVM/FetVM/or VTVM.
While evaluating in that output stage, also check for dried out cathode bypass electrolytics C131/C171 onV104/110 12AX7 preamps.
At the amps very front end, receiving the cartridges input, are the 2 “geranium” xstrs with their suspect C102/C140 electrolytic couplers along with emitter bypass caps C103/C141 and C106/C144. After SS/ to/ tube interfacing into V101/108 12AX7’s the coupling caps C110/C150 C121/C160 are the most critical along with a series string of couplers C112/C113/C116/C118 and C151/C154/156 of less import, but still in the loop.
On the front two 12AX7 stages , there could be dried out cathode bypass caps C109/C149 and C119/C157.
Lastly, on the cartridge , certainly that should use the old battleship reliable variable reluctance head unit. What you might do is see if it would be permissible to have your cartridge pulled….and with you, and see if that other boxes owner would let you sub in your unit and see if its output is on a par with that units cartridge. Your common Seeburg key should get you into the top of the other unit as typically,there was only need for the units cash box keys to be custom cut.
References:
http://www.zeikpagina.nl/jsales/schemas/seeburg/shfa1
Seeburg Power Amp ..front end ….output stage
http://www.zeikpagina.nl/jsales/schemas/seeburg/shfa1a
Seeburg Power Amp ..Tubed Power ….output stage<p>73's de Edd
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;) ;)<p>[ October 07, 2004: Message edited by: Edd Whatley ]</p>

toejam
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Re: seeburg amp question

Post by toejam » Thu Oct 07, 2004 2:55 pm

does that lp1 use a tormat?

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ModRob
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Re: seeburg amp question

Post by ModRob » Thu Oct 07, 2004 4:43 pm

Yes sir, the LP1 uses the Tormat "system"...

paulrevelcet
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Re: seeburg amp question

Post by paulrevelcet » Thu Oct 07, 2004 5:07 pm

The model number is a Select-o-matic 220, not sure of the age.
<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>does that lp1 use a tormat? <hr></blockquote> Yes it does,A TSU1.
I borrowed the restaurant owners amp and put it in my box, it was about 60% louder, I put mine back in and swapped all the tubes just in case my new tubes were not so new, did not hear any difference,so that rules out the head unit and speakers,or anything in between, so now I know its in the amp its self. I just put a complete cap kit in it so I may have put the wrong value in the wrong place, but Im sure that they are all new.<p>
What would be the best way to get the 5U4G-b to power on without the amp being in the jukebox? I have a hard time getting down in the floor and would like to trouble shoot in on my bench, I think the selector trips a relay to make the tube come on? They had trouble with the tube burning out so they made it only come on when needed.<p>Edd, could you out line each stage for me, for example I know the audio comes into Q101,2,3,4 and then into V101,V108 through C107, but not sure of the levels of each stage, I guess what i'm looking for is a block diagram of the amp, I will try all the things in your post, When I get the 5U4G-b powered up on my bench. thanks everyone.

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Re: seeburg amp question

Post by Enzo » Thu Oct 07, 2004 7:11 pm

If A sides and B sides are the same volume, then the cartridge is OK, Those are dual cartridges - a separate unit for each side in a common housing. All the more so when the other amp works OK with this cart.<p>The 220 is a nice old box, lots of chrome.<p>The two channels share little beyond power supply and mute/squelch, so if both channels are diminished, it is not likely some circuit part, especially if you have replaced the caps. My suspicion is it might be stuck in mute somehow. Or that there is a problem with the volume control. Another thing to check is the -22VDC supply the xstrs run on. it derives off the -35VDC bias supply.<p>SInce another amp works better, we can rule out stick switch on the mechanism - the one that mures the amp during scan.<p>If you have the schematic, there are DC voltages on it and AC signal levels on at least the first half. The original schematic has a block diaggram, but if yours is a reprint it may just have the schemo only.<p>The two channel mute slide switches work by grounding off the signal as it comes out of the preamp and just before the volume control. This is a handy point to look for preamp output as well as inject signal.<p>I work on these enough I have a bench rig for them. I will measure it here. It is a wood plank 7x20" - about the size of the Seeburg chassis ignoring the mounting ears. Widrh doesn't matter, get the length right. Wide enough to be stable. Screwed to it at each end is a metal bracket I dug up. Flat hunk of metal about 6" wide with a right angle bend along one end. The little right angle part is where the screws go, and the thing then sticks up from the plank about 7-8". Sitting on the bench it is a wide U shaped thing - the plank with a vertical part sticking up on each end. It is a cradle on which I sit the amp chassis. The chassis mounting ears sit on the metal brackets with the tubes hanging down underneath. Obvious to look at, clumsy to describe, extremely simple.<p>The amp needs from external source both 6VAC and 120VAC. The heaters are always on so the tubes are always ready. The 120VAC is for the B+ system and it is only powered up when the mechanism is energized. If the mech motor is running, the amp is on, and when the mech rests, the amp turns off - except the heaters.<p>Then to power it up, there is the four blade Cinch-Jones plug. Two blades are 6.3VAC for the tube heaters, and the other two blades are 120VAC for the works. The 120VAC is fused, but the heaters are not. I have a female connector to mate this, with a plain old 2-wire line cord coming out for the 120VAC. I also have a pair of wires coming out with banana plugs to mate with my bench 6VAC supply. <p>To make yours, you need to get 6.3VAC and 120VAC to those four blades. Make up a thing like mine or use clip leads. I think the Cinch plug is a 400 series. I am not sure if the current 2400 series is compatible or not, looks like it. If you are not planning a bunch of them, use clips.<p>All the Seeburg chassis of that era were the same size, and they all mated the same Cinch connector, so my setup was effectively universal.<p>You will also have to make a couple other connections. Both channels need to have a load - speaker or resistor. And look at the 6 pin plastic speaker connector. It is where the wires to the jukebox speakers go, but there is also a jumper that grounds the center tap of the HV winding of the power transformer. Unplug that and there is no B+. A clip lead to chassis to ground the center tap and you are running.

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Re: seeburg amp question

Post by toejam » Fri Oct 08, 2004 6:51 am

modrob:
the main reason tormat models lose selection to one side is due to a loose connection on one of the contacts that slide on the long contacts on the tormat. there is a wire going to each one of them and you can reconnect them on your back. Give aech one a little pull and the pin should move down freely, some times they can sieze and that would be a problem also.
good luck
tj

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Re: seeburg amp question

Post by paulrevelcet » Sat Oct 09, 2004 8:47 pm

thanks everyone, as soon as I get some time this weekend, I will try everyone's suggestion, will let you know what I come up with. One more thing I have noticed is that the base control doesn`t seem to work.<p>[ October 09, 2004: Message edited by: paulrevelcet ]</p>

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