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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders. |
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30th Nov 2021, 12:54 pm | #21 |
Octode
Join Date: Jan 2009
Location: Falmouth, Cornwall, UK.
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Re: Taylor 65B Sig Generator: Dodgy Waveform
Could you take a picture of the waveform from the right hand socket, would be interesting to see how they compare.
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Stephen _________"It`s only an old telly" ___ |
30th Nov 2021, 3:09 pm | #22 |
Pentode
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Location: Staines-Upon-Thames, Surrey, UK.
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Re: Taylor 65B Sig Generator: Dodgy Waveform
Audio Output from Taylor 65B
As you can see, it's a nice clean waveform. The unmodulated RF is similarly clean. It's just the mixture of the two that's off! |
30th Nov 2021, 4:27 pm | #23 | |
Dekatron
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
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Re: Taylor 65B Sig Generator: Dodgy Waveform
Quote:
It would be useful to compare the modulated HT of the two SG's. |
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30th Nov 2021, 4:34 pm | #24 |
Octode
Join Date: Jan 2009
Location: Falmouth, Cornwall, UK.
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Re: Taylor 65B Sig Generator: Dodgy Waveform
Think its hidden in the shielded output connector block, been quite some time since I was inside mine.
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Stephen _________"It`s only an old telly" ___ |
30th Nov 2021, 6:45 pm | #25 | |
Pentode
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Location: Staines-Upon-Thames, Surrey, UK.
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Re: Taylor 65B Sig Generator: Dodgy Waveform
Yes, I replaced the 0.01uF output capacitor.
In fact, I replaced all the caps except for C5 (500pF) & C6 (2nF). Quote:
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30th Nov 2021, 6:50 pm | #26 | |
Pentode
Join Date: Oct 2016
Location: Maldon, Essex, UK.
Posts: 182
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Re: Taylor 65B Sig Generator: Dodgy Waveform
Quote:
You could try connecting a resistor (say about 2 kΩ) between the RF Output and ground so that C7 acts as a high pass filter. This might make the waveform look more symmetrical but is unlikely to make any difference to a receiver under test because the circuits are tuned to attenuate frequencies other than the one to which it is being tuned. The photographs show examples of the modulated waveforms on my Windsor 65c. There is a big variation depending on the frequency with the amplitude decreasing at higher frequencies. The upper channel is the slider of the fine attenuator and the lower channel is the RF output with the attenuators at maximum. Both channels were set to 0.2 V/div. The last photo shows both inputs at GND so that the negative bias mentioned in post #12 can be judged in the other photographs. David Last edited by Neutrino; 30th Nov 2021 at 6:59 pm. Reason: Typo |
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30th Nov 2021, 7:24 pm | #27 |
Heptode
Join Date: Jul 2018
Location: Worthing, West Sussex, UK.
Posts: 994
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Re: Taylor 65B Sig Generator: Dodgy Waveform
Can you not try a resistive load for the modulator (you may need to use a coupling cap to not start to short any HT) that way you should see the AF wave and see how it behaves loaded when compared to actually modulating the oscillator - at least that way you can confirm that the AF stage/modulator and the Modulation transformer are OK.
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1st Dec 2021, 8:19 pm | #28 |
Pentode
Join Date: Dec 2017
Location: Staines-Upon-Thames, Surrey, UK.
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Re: Taylor 65B Sig Generator: Dodgy Waveform
Thanks David (Neutrino) for the filter idea.
As suggested, I added the resistor at the output and the wave shape is greatly improved as shown below... |
1st Dec 2021, 8:31 pm | #29 |
Octode
Join Date: Jan 2009
Location: Falmouth, Cornwall, UK.
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Re: Taylor 65B Sig Generator: Dodgy Waveform
If you changed VR2 that should measure 2K but actually measures 6k8 it would also remedy the situation ?
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Stephen _________"It`s only an old telly" ___ |
1st Dec 2021, 10:59 pm | #30 |
Dekatron
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
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Re: Taylor 65B Sig Generator: Dodgy Waveform
Changing VR2 won't fix it but it should not be a problem in normal use. As already said, these are basic signal generators for radio alignment, a professional SG would have a known fixed output impedance but here it is all over the place.
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2nd Dec 2021, 11:38 pm | #31 |
Hexode
Join Date: Apr 2017
Location: Buderim, Queensland, Australia.
Posts: 428
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Re: Taylor 65B Sig Generator: Dodgy Waveform
Just possibly, you made a slightly rash judgement on the emission capability of rectifier V1 6X5 in post #8?
Have you changed it with a known good valve? Try temporarily plonking (technical term) two 1N4004, 7, etc, across the anode to cathode of V1; you can leave the valve in circuit. Conditions apply. Pls report back on this specific test. |
3rd Dec 2021, 12:03 am | #32 |
Pentode
Join Date: Dec 2017
Location: Staines-Upon-Thames, Surrey, UK.
Posts: 122
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Re: Taylor 65B Sig Generator: Dodgy Waveform
Thanks Radio1950 - I'll hold fire on the silicon diodes right now as I should have a new V1 6X5 to try by Saturday. Let's see if that changes anything. I also hope to get all the valves tested this weekend. I'll let you know how it goes.
Freya - VR2 was quite hard to reach so I may have misread the value at 6K. I'll double-check it tomorrow and report back. |
3rd Dec 2021, 4:48 am | #33 |
Hexode
Join Date: Apr 2017
Location: Buderim, Queensland, Australia.
Posts: 428
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Re: Taylor 65B Sig Generator: Dodgy Waveform
Meanwhile, if you get bored, or if postie is late ...
Brutal option follows! You could just - . lift pos end of C4 C5 . probe cathode of V1 6X5 with CRO, using resistive divider if necessary . DVM cathode V1 to earth . warm up 2 mins . observe CRO to see full wave rectified AC with symmetrical humps. If not, it is probably low emission of one half of V1, or crook pwr transf or crook wiring joint. . power down, restore C4 C5 . warm up 2 mins . short junction of R1 and mod transformer to earth momentarily, with your choice of 100R or (insulated) screwdriver. . measure volts V1 cathode to earth, including resistance of 100R or screwdriver. . do maths to get mA DC from V1. . the DVM will read approx average DC volts . compare with V1 spec sheet. . expect 35 mA or so If low current, V1 is suspect or crook wiring. By the way, can you (hand on heart) confirm the power transf pri tap is set for your local mains voltage, and that valves have a measured 6.3 V on heaters please? . Last edited by Radio1950; 3rd Dec 2021 at 4:49 am. Reason: I am in two minds as to whether to cut it all |
3rd Dec 2021, 5:17 pm | #34 |
Pentode
Join Date: Dec 2017
Location: Staines-Upon-Thames, Surrey, UK.
Posts: 122
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Re: Taylor 65B Sig Generator: Dodgy Waveform
Hi 1950,
I disconnected the smoothing caps as suggested. (I assume that's what you meant, they are C1 C2, or C5 C6, depending on which cct diagram). The photos below show the input (anode) and output (cathode) waveforms. So it appears that we have half-wave rectification! Just checked the wiring on V1 and the 2 anodes are connected together. Is this wrong? The diagram below which I think comes from the Taylor Instruction Manual shows the anodes to be separate and connected across the transformer secondary. By the way, the transformer primary is set for 240v. V2 heater is 6.7v ac. |
3rd Dec 2021, 5:44 pm | #35 |
Octode
Join Date: Jan 2009
Location: Falmouth, Cornwall, UK.
Posts: 1,990
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Re: Taylor 65B Sig Generator: Dodgy Waveform
If it helps, on mine the anodes are both connected to separate tags on the transformer.
__________________
Stephen _________"It`s only an old telly" ___ |
3rd Dec 2021, 8:18 pm | #36 |
Pentode
Join Date: Oct 2016
Location: Maldon, Essex, UK.
Posts: 182
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Re: Taylor 65B Sig Generator: Dodgy Waveform
My Windsor 65c has the anodes connected together as shown in the diagram in the link. I suppose that there is a small cost saving on the transformer.
https://www.vintage-radio.net/forum/...2&postcount=11 My Windsor 65c is accurate to within 1% up to 8 MHZ and within about 2% up to 80 MHz which I think is remarkably good for and instrument of this age. It has a well shielded attenuator so that the RF output can be adjusted to a low level and a filter on the mains supply to prevent R.F. leaking though the mains cable. This is what was needed in a radio service department to align AM receivers. I agree with post #13. Don’t worry about the waveform if your Taylor 65B produces an R.F. output reasonably close to the correct frequency. David |
3rd Dec 2021, 11:50 pm | #37 |
Pentode
Join Date: Dec 2017
Location: Staines-Upon-Thames, Surrey, UK.
Posts: 122
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Re: Taylor 65B Sig Generator: Dodgy Waveform
Thanks Stephen & Neutrino.
I can't imagine that the rectification (half or full) matters that much, as long as the HT is at the right voltage and current, and the ripple is low. Anyhow, the new rectifier arrived today and it seems to have improved the output - see screenshot below. This is probably as good as it gets, so let's call it a day. A big thank you to everyone that contributed to the discussion. Howard |
4th Dec 2021, 12:37 am | #38 |
Hexode
Join Date: Apr 2017
Location: Buderim, Queensland, Australia.
Posts: 428
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Re: Taylor 65B Sig Generator: Dodgy Waveform
One last optional request please, no screwdrivers involved.
Can you set freq to 1 MHz, MOD ON, and probe the oscillator anode with 10X. Click! Just curious. . |
4th Dec 2021, 5:01 pm | #39 |
Pentode
Join Date: Dec 2017
Location: Staines-Upon-Thames, Surrey, UK.
Posts: 122
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Re: Taylor 65B Sig Generator: Dodgy Waveform
Hi 1950,
Sorry, but I can't do the 1 Mhz test at the moment. I'm currently investigating the power supply section and it's all in bits at the moment. The mains transformer seems to have developed a fault at some point. The centre tap is open-circuit. As a workaround, someone has re-wired this section. The anodes of V1 have been joined together and are fed by one end of the transformer. The other end of the transformer has been grounded. The net result of this is that V1 is now acting as a half-wave instead of a full-wave rectifier. I thought this wasn't a problem, but on second thoughts, it might be. What's the ac voltage across the anodes on your one? I measured 194v at V1 cathode and 75 volts across R1 (194 - 119) which gives 7.5 mA. How does this compare to your set? By the way, the valves have been tested and are all good with emissions of 80-90% Does anyone have a suitable replacement transformer? |
4th Dec 2021, 6:12 pm | #40 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: Taylor 65B Sig Generator: Dodgy Waveform
Re: Open circuit center tap....Screen connection ?:
https://www.vintage-radio.net/forum/...2&d=1416775292 https://www.vintage-radio.net/forum/...d.php?t=111474 Lawrence. Last edited by ms660; 4th Dec 2021 at 6:31 pm. Reason: link added and re-write |