10th Aug 2012, 9:47 pm | #121 |
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Re: Bush SRP 31D not producing sound.
I suggest you take voltage readings on all valves again. With the experience you'll have gained after 120 posts, you should now know what readings to expect.
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11th Aug 2012, 10:05 pm | #122 |
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Re: Bush SRP 31D not producing sound.
taken readings from the valves and they are a lot different I'm afraid.. AC/HL said the readings from the valves should be:
1- 0v (Control Grid Triode) 2- 1.5v (V2- 25v) (Cathode Triode) 3- 190v (Screen Grid Pentode) 6- 210v (Anode Pentode) 7- 5.6v (Cathode Pentode) 8- 0v (Control Grid Pentode) 9- 125v (V2- 170v) (Anode Triode) I have some different values now and some of them changed when I re tested the dodgy ones too! 1- 0v (V2- 26.8v then on retest 0v) (Control Grid Triode) 2- 8.1v (V2- 168.9v then 0v on retest) (Cathode Triode) 3- 193v (Screen Grid Pentode) 6- 214v (Anode Pentode) 7- 37.5v (V2- was also 37.5 but then turned to 7.02 on retest) (Cathode Pentode) 8- 0v (Control Grid Pentode) 9- 113v (V2- 165v and V1 changed to 123v on retest) (Anode Triode) so as you can see some of the pins are now proving dodgy... Last edited by Station X; 12th Aug 2012 at 9:36 pm. Reason: Electrode designations added. |
12th Aug 2012, 9:58 pm | #123 |
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Re: Bush SRP 31D not producing sound.
I think we established some time back in the thread that V2, being a phase splitter, should have a positive voltage on its control grid. Something approaching 23V I'd say. This is not reflected in AC/HL's figures.
If you really saw 168.9V on the cathode of V2, then this points to a failure of C5, or more likely a contact between, say pins 1 and 9. Pins 3 should be at the same voltage on both valves because they're tied together. Ditto pins 7 I wouldn't expect to see much difference in the pins 6 readings either. I'd make sure that all valveholders are making good contact with their valve pins. Stick to one set of valves, and get a stable set of readings before posting again.
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13th Aug 2012, 6:25 pm | #124 |
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Re: Bush SRP 31D not producing sound.
made sure the valves were sitting nicely in their new holders and tested four times (turning the machine on and off each time and letting the valves warm up) found that my readings for V2 were consistently:
Control Grid Triode- 26.8 Cathode Triode- 168.5 Screen Grid Pentode- 190 Anode Pentode- 214 Cathode Pentode- 36.2 Control Grid Pentode- 0.01 Anode Triode- 163 I also had a test of V1 a couple of times: Control Grid Triode- 0 Cathode Triode- 8.1 Screen Grid Pentode- 207 Anode Pentode- 218 Cathode Pentode- 30.4 Control Grid Pentode- 0.01 Anode Triode- 123 |
13th Aug 2012, 7:52 pm | #125 |
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Re: Bush SRP 31D not producing sound.
also, just an update. I put a new cable to replace theconnection from the turntable to amp and I did get sound interestingly enough but it is really bad sound quality... sounds muffled and only certain notes are being played and a lot quieter than it used to... could this be down to the Cathode Triode's 168v and Cathode Pentode's 36.2v?
would like to add that when changing valve holders I did break a few resistors but I replaced them with modern equivelants, I made sure they were 1/4 watt resistors at the right ohm levels, some though were replaced with metal film resistors at 0.6w and at the right ohms. I was told by maplin that 0.6 will replace 1/4 watt... they are tiny in comparison to the old ones though!! |
13th Aug 2012, 8:43 pm | #126 |
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Re: Bush SRP 31D not producing sound.
Check your wiring. I wonder if there's a wire wrong somewhere. The valve V1 looks OK, but V2 looks well off what it should be. The triode side should have volts on the Anode but not the grid. There should be lower volts on the Cathodes.
Funny thing is, the Cathode is higher than the Anode, which will not work! Cheers, Steve P.
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13th Aug 2012, 9:13 pm | #127 | |
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Re: Bush SRP 31D not producing sound.
Quote:
Circuit here:- https://www.vintage-radio.net/forum/...ad.php?t=86032 It should be impossible for the screen grids and cathodes of the output pentode valves to be at different voltages, because they're wired together. Clearly the contact twixt one valveholder and valve pin must be dodgy. I can't get my head round 168V on the cathode. There must be a misplaced wire or a short circuit somewhere. Are you sure that your new resistors are the correct value? Check the colour codes and measure them with your meter.
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13th Aug 2012, 10:16 pm | #128 |
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Re: Bush SRP 31D not producing sound.
Yes. I agree with Graham. 168Von the cathode is clearly wrong as the circuit shows 25V. Make sure that R10 is 2.7K and not 27K (or even 270K)! Colours should be red violet red and whatever tolerance the resistor is (silver or gold). Measure it with your meter if uncertain. It's worth checking R8 as well which should be 47K (yellow, violet, orange). With 168 volts on the cathode, the valve is not drawing any current...no wonder it sounds bad!
Either of these resistor being too high in value will result in the cathode voltage rising. Rich.
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13th Aug 2012, 10:52 pm | #129 |
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Re: Bush SRP 31D not producing sound.
I think Graham's reference to the circuit is extremely relevant. The circuit has expected voltages at various points shown on it. The grid of V2a can be interpolated from the 25V cathode voltage and the potential divider R10 R8 as 23.6V. Unfortunately some of the voltages look as though they relate to measurements with a specific meter, otherwise, for example, it makes no sense that the cathode of V2a is 25V above 0V whereas its anode is only 20V below HT+.
Checking R values by measurement is also important as mentioned. I note you have used some modern resistors- there is one very important trap for the unwary with these, many modern close tolerance resistors have 4-band codes on them which to the quick glance look factors of ten too low. For instance a 4-band 47K will be yellow violet black red (4 7 0 plus 2-0s = 47000) plus tolerance (probably 1 or 2 %) plus maybe tempco as well. An unsuspecting glance could read it as 470R 2%! There's also the problem of codes that look plausible backwards as well as forwards- codes like Bn Rd Bk Bk Bn (120R 1%) reads backwards as 10K 1%! BTDT at work (wrong values from supplier ). Fear not, it will work eventually!
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15th Aug 2012, 5:04 pm | #130 |
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Re: Bush SRP 31D not producing sound.
The resistors are the right colour coding. Some have the 5 band system and some arre the usual 4 band. The tolerances aren't what it specifies in the circuit, most have gold bands but the ones from Maplin (0.6w metal films) are brown band as opposed to the no band 20% tolerance. I tried to test with my multimeter but it doesn't like testing resistance it seems. I don't get it, it only works on the 2000k setting and spits out random nonsense numbers which I'm not happy with, definitely not! Although it would be too odd for the resistors all to be out as there are three and I tested some spares I had from another company. Also one of the old ones that I replaced was intact and it did the same thing!
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15th Aug 2012, 7:35 pm | #131 |
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Re: Bush SRP 31D not producing sound.
A brown band indicates 1% tolerance, so there'll be no problems there.
I assume you're measuring the resistors in circuit? If so you need to allow time for the reading to settle. Initially a low resistance will be indictated as capacitors in the circuit will be charged by the meter's battery. Once the caps are charged a true reading will be given. If unsure of the value, start on the highest range and work down until a sensible reading is given.
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16th Aug 2012, 10:48 am | #132 |
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Re: Bush SRP 31D not producing sound.
As Graham said, you need to disconnect the resistor from circuit, at least one end. Also, don't hold the probes onto the component with fingers as typical skin resistance of 500 - 1000 K ohms might affect your high value resistance readings. Make sure you have good conenctions from the probes to the resisitors
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17th Aug 2012, 3:11 pm | #133 |
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Re: Bush SRP 31D not producing sound.
it seems my multimeter just doesn't understand resistance, told my dad about it and he tried it and told me its acting up, don't understand how though! how ironic! but in regards to the resistors thewy are all new and some were different manufacture as i ordered a couple the same by accident and it all has the same effect. I also changed C5 like Graham suggested could be acting up (swapped it with one in my SRP31) same story however. I did have a period when the V1 valve holder was replaced but the one for V2 wasn't and it did work perfectly but I decided to change it anyway and now its doing this. From what I can see I have wired it right (used a photo of it beforehand to reassemble connections)... here's the photos of it then and now... awful soldering I know
http://s2.photobucket.com/albums/y8/...t=IMGP0499.jpg before changing holder http://s2.photobucket.com/albums/y8/...t=IMGP0506.jpg after changing holder |
17th Aug 2012, 4:26 pm | #134 |
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Re: Bush SRP 31D not producing sound.
Hi,
Beware, in the second photo, the insulation to the earth is dammaged and the live appears to have a chunk out of it in close proximity. Look also for dry joints. These days with lead free solder, the joints do not have the shiny appearance that you used to obtain but they should not look too dull. Keep everything clean before solder is appied and it should flow better. The connections appear okay from what I can see. Rob |
17th Aug 2012, 5:08 pm | #135 |
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Re: Bush SRP 31D not producing sound.
A few observations.
If your meter doesn't understand resistance, how do you know it understands volts? Perhaps you should get a better one? In the "before" picture you show a red/yellow/black Plessey electrolytic (C4?) in parallel with a resistor (R5?). In the after picture I can't see a resistor. If it's there, is it coded red, red, red? You reallly should replace the other Plessey capacitor. They're well past their sell by date.
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17th Aug 2012, 7:38 pm | #136 |
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Re: Bush SRP 31D not producing sound.
It looks like a resistor is under the cap.
P.S. 1 Watt resistors 'fit in' better as they are of a similar size to the old ones you are replacing. They also have a much higher maximum working voltage. Last edited by matthewhouse; 17th Aug 2012 at 7:47 pm. |
17th Aug 2012, 8:44 pm | #137 |
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Re: Bush SRP 31D not producing sound.
resistor is still there and is the triple red band, its just hiding under the new capacitor is all. The capacitor I used was 47uf 16v... the old plessley one was 50uf 12v although I hear it shouldn't be an issue, hopefully that's right! haha. As for the multimeter, I was given £10 vouchers by the local maplins randomly so I might redeem them and buy a £20 multimeter I saw, saves me £10 I guess and will hopefully be more reliable
as for the resistors, is it ok that they are that size? because I just assumed that somehow 1/4w resistors had just gotten smaller since the 60s to accommodate micro-electronics and circuit boards and such. Should I be thinking about buying ones to match the size like Matthewhouse advises? |
18th Aug 2012, 9:10 am | #138 |
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Re: Bush SRP 31D not producing sound.
We're not getting very far very fast with this.
It's the 168V on V2 triode cathode that's most difficult to understand. Could you measure the voltages across R7, R8 and R10 please and post the results.
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18th Aug 2012, 7:19 pm | #139 |
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Re: Bush SRP 31D not producing sound.
I bought a new multimeter Precision Gold PG017... dunno if its particularly good but looks good from what I've seen... Resistors all seem correct value although the 5.6k on the 20k setting is reading at 0.56... I assume this means I was sold a 560 ohm resistor by accident? surely though if its meant to read 0v on that pin then it should be ok regardless? In regards to V2, I have different readings! So my readings are as follows:
Control Grid Triode- 15.5 Cathode Triode- 25.7 Screen Grid Pentode- 197 Anode Pentode- 215 Cathode Pentode- 5.19 Control Grid Pentode- 0 Anode Triode- 172 I also made a discovery when reading the Control Grid Triode the machine did its phasing out thing... the horrible buzz it now makes went down and I noticed the voltage reading drop slowly from 15.5v to 0.00v and I brushed the stylus and there was no reaction in regards to sound, then when I tried to test it again, the grid slowly regained its 15v and it was live again. Played a record on it and have noticed it's noticeably quieter than it used to be and not as good quality as it used to be. |
18th Aug 2012, 10:45 pm | #140 |
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Re: Bush SRP 31D not producing sound.
A wrong value resistor could easily affect the sound, so get it replaced with the right one (5.6 kΩ is green, blue, black, brown or green, blue, red) and try again. This probably won't cure the other, intermittent fault, but hopefully it will work better when it is working.
It certainly sounds like there was a problem with your old meter. Don't chuck it just yet, though! It might be nothing worse than a poor connection on one of the probes, or a spent battery. Try it with the leads from the new one, if they fit. If you have to open it up to swap the battery, check for dry joints on the probe sockets.
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