seeburg amp question

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paulrevelcet
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Re: seeburg amp question

Post by paulrevelcet » Sun Oct 10, 2004 6:28 am

I got my rig built and everything is on, I have my speakers hooked up and now what level of signal do I need to inject straight into j101 and what do I need to build to do this. What do you normally do enzo?

Enzo
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Re: seeburg amp question

Post by Enzo » Sun Oct 10, 2004 10:19 am

If your schematic is remotely like mine, look on the left, right next to the input jack. The AC signal voltage at the input looks like 5mv. Also, note 1 nearby mentions that it is a 1000cps signal. cps was how we used to describe frequency. We now use Hz. 1000cps = 1000Hz = 1kHz.<p>You won't like my test setup. I touch the input jacks with something to introduce hum as a test signal. My finger, a screwdriver, my meter probe. When I just want the thing to pass a signal, that's all I need. Sometimes I use the signal from my bench stereo as an input, even though it is meant for phono cartridge. Once I am ready for final check, I plug a plain old vanilla turntable into it.<p>Once I am on the bench, the first thing I do is verify the DC voltages are somewhat close. Mostly I am looking for leaky paper caps. DC on the wrong ends. Get the volts right on the grids and the rest falls into place.<p>On stereo amps I usually input to one side and short the sides together with a clip lead to insure the exact same input to both channels for proper comparisons.<p>If the bass control is inop, make sure the switch contacts are making, use an ohm meter. Then check the caps. If they are real leaky, it will swamp their effect, and also your signal level. When you max the switch, only C126 and C129 remain in circuit. Reducing bass setting adds more caps.

paulrevelcet
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Re: seeburg amp question

Post by paulrevelcet » Mon Oct 11, 2004 4:53 pm

I started out with channel 1 being very low and in the process of testing I found I had no voltage on q102, bad wire, problem solved, now channel 2 way lower than channel 1, I didnt realize how bad a shape both channels were in, now that I have something to compare with, I am convinced that channel 1 is perfect, now on with channel two.<p>using a small cd player with a meter probe hooked to the headphone jack, and adjusting the volume according to where I inject the signal, when a signal is injected at C160 and C121 both channels sound great, when a signal is injected at C146 and C107 channel 2 is severely attenuated, so that means I have a problem in V108? I checked the voltages on both and they are almost the same,with no signal impute here are the voltages.<p>Pin 1 300v, Pin 2 thru 5 no voltage, Pin 6 246v, Pin 7 ov of course, Pin 8 1.7v not sure what to do next, I haven't really studied the theory of tubes so I am lost. thanks for all the help.

Enzo
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Re: seeburg amp question

Post by Enzo » Mon Oct 11, 2004 8:55 pm

Now we are getting somewhere. Getting the one problem out of the way opened your window.<p>V108 is where the trouble lies alright. First swap it with V101 and see if the problem moves with it.<p>Pin 1 is the plate of that triode and 300V is too high. Pin 2 should have no DC, but pin 3 ought to have 2-3VDC. The fact that there is zero there means the tube is not conducting. That also explains the high plate voltage. With no current flowing through the tube, no current flows through R186, so no voltage drops along R186. That is classic tube troubleshooting - high plate volts and no cathode volts means a dead tube.<p>Pins 4 and 5 are the heaters - along with pin 9. They have no reference to ground,so they measure no voltage to it.<p>Pins 6,7,8 are the other triode and the voltages seem OK to me. You can always compare to the other channel.<p>You may merely have a bad tube. With almost the same spot in the circuit dead in both channels - though for different reasons - no wonder the two sounded poorly alike.<p>It could also be a bad tube socket, but I am betting on the tube

paulrevelcet
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Re: seeburg amp question

Post by paulrevelcet » Tue Oct 12, 2004 5:11 am

Switching the tubs had no effect, so bad tube socket? how does the voltage on pin 3 develop? I hav e some tube sockets so I will change it today, and will let you know what happens. Thanks Enzo.

paulrevelcet
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Re: seeburg amp question

Post by paulrevelcet » Tue Oct 12, 2004 6:06 am

changed the tube socket, it done the trick as far as the voltage on pin 3, I now have 2.5 volts, but it made no difference what so ever in the sound level, but I feel that were getting closer, I rechecked all the voltage levels and now there spot on, 300v fell to 270. could there be any thing in the squelch circuit that would be shorting my signal to ground?

paulrevelcet
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Re: seeburg amp question

Post by paulrevelcet » Tue Oct 12, 2004 12:33 pm

You know that old saying, just because there new parts don't mean there good parts, C154 was bad and C151 was bad, went through all that for a bad tube socket and 2 bad caps. Thanks Enzo, without your help I would have given up and tried to find a working amp for sale, but now not only have I increased my skill at reading schematics, but I feel confident enough to restore more jukeboxes.

Enzo
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Re: seeburg amp question

Post by Enzo » Tue Oct 12, 2004 4:15 pm

Cool, I am glad it works. It is usually bad caps in these. I find it interesting that in jukebox amps I mostly replace caps, but in guitar amps I rarely have to replace caps. AMps of the same vintage.<p>There is a whole world of juke boxes out there.<p>If you ever need assistance with them, you can email me by writing to<p>"tmenzo" then the symbol for "at" then "msn" followed by the dot com. If you get me.<p>Good luck

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Edd
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Re: seeburg amp question

Post by Edd » Sat Oct 23, 2004 12:02 pm

Referencing to your query on the stage gain through the Seeburger’s audio amp stages, here is a reference signal source to inject at the cartridge input connector of the unit (J101), thus enabling you to trace the audio signal through the amp and note the gain in each stage, from frontal SS preamp stages, on thru to its output, checking the AC voltage level at sequential inputs and outputs of each gain block.
With the J-boxes amp being of a hybrid design, by all means use a short leaded DC blocking/coupling capacitor (.1-1ufd range), with one end spiraled around the hot AC test lead probe.(Of adequate P-P voltage rating to exceed the highest voltage level to be probed). This should enable extracting a DC’less non ambiguous reading even in probing the first stages where, when using the typical ~3 ft unshielded leads of DVMs, you will also be injecting stray 60~ in addition, into the down line circuitry. The AC voltage reading up to that point should not have been influenced by the stray level, enabling the reading of stage gain(s) up to that probe point.
With an initial check confirming that all vol control,balance, tone settings and speaker loading are duplicated between the two amps being compared, the gain readings should be in accordance…that is… unless the amp has deficient components causing the gain problems.
Aside…. You also might want to muffle the speaker outputs with some pillows or just inject the test signal only at times of test readings, with a grounding test clip to J101 being lifted.<p>A sequence of test probe points would be starting at the front end:
Q101 Coll, Q102 Base, Q102 Coll, V101 #7, V101 #6, V101 #2, V101 #1, V103 #2, V103#1, V103#7, V103#8, (Cath Foll) V104#7, V104#6, V104#2, V104 #1&3 (Bal drive outs), V105/106 #3 or 6 (Power out grids). Duplicate readings then to be taken and compared against the other channels amp. Also a checking of the diminishing of signal level on stages using emitter or cathode bypassing electrolytics should attest to their effectiveness.(C119, C106, C131, C103(in neg f/b tone loop)<p>The initial use of the injected CD audio source would certainly suffice for rough go-no go audio stage testing, but somehow I suspicion that you had neither a lab quality HP/Tek/Wavetek Audio Oscillator with its adjustable attenuation level down into the low MV levels…or even an old HP 200C/D series.
The referenced osc below was what I used to build into push to talk mike housings of commercial business band Fm mobile radio xmitters
waaay back in their first days, where conventional squelch was adequate, that is, until multiple users shared a common freq. Thereby creating quite a bit of unwanted extraneous background chatter to users. The use of an initial tone burst of the transmission engaged the receivers secondary tone squelch decoder using LC discrimination constants. The end result was having the system squelch lockout/performance as quiet as a crypt keepers tomb. Later times , I even used it to better advantage on definitely crowded CB freqs.
The circuit below uses values selected towards very common EIA values that should be easy to find. The resulting frequency falls in the order of the high 400~ range…in accordance to the transistors gain as well as parts tolerances….rather than the purist audio test freqs of 400~ and 1 Kc, but it will fulfill the requirement of a stable low level sine output .
The circuit can be built up on about a 2 in square, cut from an eng breadboard copper grid matrix. The unit will not pose any power ground loops due to being 9 V batt powered and a switch is optional, with power drain being just a few ma’s. Unplugging the battery may be a viable switch, since the unit might typically get infrequent use.
The unit also needs to be built in a small metal shielded case/or soldered copper PCB stock with minimally exposed Hot sig output lead length, unless one opts to use a shielded lead output line with its breakout from the concentric shielding made within the last ¼ inch or so.
BTW on your discovered def “new” capacitors, were they bad enough on leakage as to be read with an ohmmeter or did it take the DC leakage/metered DC voltage presence type of test to detect them?
Schematic References Utilized:
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>[ February 20, 2005: Message edited by: Edd Whatley ]</p>

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