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Old 13th May 2022, 1:15 pm   #1
Peterdee
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Location: Poole, Dorsetshire, UK.
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Default Heathkit HG10-B VFO

Hi again all
Here is my latest problem so I hope someone has some advice on this vfo.
I just purchased above vfo to use with my HW16 tcvr. Assured it works fine, and have done some voltage checks to the circuit diagram and they are all high.
V1 pin1 120v, cct says 57v pin 2 170v cct says 108v pin 3 167v cct says 90v etc. I did the test in stby mode on 80m.
With the vfo connected to the tcvr, it keys up ok, spots ok but I lose power. Without the vfo connected I have a good 40w out, but with vfo in only 20w full power, and which key jack should I use? The jack on the vfo produces nothing at key down, but with key plugged into the tcvr I get the above low power out.
On the octal outlet on the tcvr there is 266v ht 5.1v heaters and -65v. The power supply I am using is 110v.
On inspection the vfo looks in good shape, no sign of any fiddling and no sign of any worn out looking components.
So, that's it, I hope someone can throw some light on the problem. As the rig is working ok, and the vfo seems to be ok the only thought I have is maybe the ac voltage too low, because I think the rig should produce 300v at the power connection and the heater voltage is quite low too.
Thanks for your time reading this and look forward to any suggestions
PeterD G0JJI
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Old 13th May 2022, 4:23 pm   #2
frsimen
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Default Re: Heathkit HG10-B VFO

The voltages in your HG10B are quite a lot higher than they should be. Is V2, the OB2 voltage stabiliser fitted and if it is, is it glowing? The HT rail within the HG10B is set by the OB2 and should be very close to 108V if the OB2 is glowing.

There should be a wire connecting pin 8 of the VFO octal socket to pin 8 of the HW16 VFO power octal socket. If this is in place, plugging the key into the HW16 key socket will operate the HG10B as intended. There is no need to plug the key into the HG10B.

Your HT and heater supplies sound rather on the low side and that may account for the lack of output.

Paula
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Old 13th May 2022, 6:07 pm   #3
Peterdee
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Default Re: Heathkit HG10-B VFO

Hi Paula
Thanks for your reply. Yes the green lead to pin 8 connected to the neon lamp which glows and then on to function switch 5. All the wiring round that area seems to be correct.
PeterD
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Old 13th May 2022, 6:33 pm   #4
frsimen
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Default Re: Heathkit HG10-B VFO

Hello Peter,

The VFO lead is wired correctly, so the key should work when plugged in to the transmitter.

Your heater voltage is almost 20% too low, much the same as the HT. Check the voltage that you are applying to the primary of the mains transformer, I expect it to be nearer 100V than 110V. It should ideally be 120V.

You didn't mention what V2, the OB2 valve is doing, that part of the circuit will be the source of trouble with the higher than expected voltages in the VFO.

Paula
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Old 13th May 2022, 9:03 pm   #5
Peterdee
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Default Re: Heathkit HG10-B VFO

Hi Paula
The transformer I have only does 110v or 150v, I think 150v might be a little too high, I know, ideally 115v would be better. Pin 4 from the tx gives 268v dc to the dropping resistor, which drops it to 108v going to pin 1 of OB2, 108v is also emitting from pin 5 of the OB2, which checks with the schematic. The valve is glowing purple, but not very bright. Not having had experience of this valve before I don't know just how bright it should be.
On the key there is only .3v in opr position, which goes on keying down.
Hope this helps
Peter
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Old 13th May 2022, 10:22 pm   #6
frsimen
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Default Re: Heathkit HG10-B VFO

Hello Peter,

So long as the OB2 is glowing and doesn't go out altogether it will be doing its job. If it should go out, the 108V rail will rise in voltage somewhat.

The odd voltage measurements that you made earlier in the VFO may have been because the OB2 wasn't glowing. There is another possibility, which is that your meter reads inaccurately in the presence of RF. Not all meters are affected in this way, but it's not unusual with digital voltmeters.

I would expect something over -100V on the key when it is up, as it is fed from the E supply (-150V). In your case, the -150V will be nearer -130V, due to the low supply voltage. 0.3V doesn't sound right and if it were what you were measuring, the PA valve would be drawing a lot of current.

The lack of output power when running from the VFO is caused by the low HT and the low heater volts. You certainly don't want to use the 150V tap on the transformer, that would be far too high an input to the HW16. You have two options, one is to source another transformer that gives a 120V output, the other is to use the trick where a fairly small low voltage transformer is used to boost the supply voltage going into the HW16. In this case, the low voltage transformer will still be quite large, perhaps 50VA, so neither option will be particularly cheap.

Paula
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Old 14th May 2022, 8:07 am   #7
Peterdee
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Default Re: Heathkit HG10-B VFO

Hi Paula
Thanks again for your advice. So the problem could be the low output in power from the hw16. I see 115v transformers on ebay rated at 200w going quite cheap, mainly for powering other low voltage equipment. Would one of those be suitable for the hw16?
Another thing that puzzles me is I have traced the 108v from R11 to pin 1 and pin 5 of V2 to pin 3 of V2 despite having passed through R1 which, I assume, should drop the v to the specified 90v. I have checked R1 in situ and it reads the 10kR that it should be. So why is it not dropping the voltage?
Sorry to be such a pain, but as you will have gathered by now my electronic knowledge is very limited!

PeterD
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Old 14th May 2022, 9:15 am   #8
frsimen
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Default Re: Heathkit HG10-B VFO

Quote:
Originally Posted by Peterdee View Post
Hi Paula
Thanks again for your advice. So the problem could be the low output in power from the hw16. I see 115v transformers on ebay rated at 200w going quite cheap, mainly for powering other low voltage equipment. Would one of those be suitable for the hw16?
Another thing that puzzles me is I have traced the 108v from R11 to pin 1 and pin 5 of V2 to pin 3 of V2 despite having passed through R1 which, I assume, should drop the v to the specified 90v. I have checked R1 in situ and it reads the 10kR that it should be. So why is it not dropping the voltage?
Sorry to be such a pain, but as you will have gathered by now my electronic knowledge is very limited!

PeterD
Hello Peter,

I'm sure the resistor is dropping the voltage. The issue is that your multimeter readings are being upset by the presence of RF at the point that you are measuring. Some meters are fine when there is RF present, others give wildly inaccurate readings, often due to their internal protection diodes which rectify the RF.

You could try soldering one end of a 100k ohm resistor to the point where you are expecting to find 90V and connect a 10nF capacitor rated at a minimum of 160V from the other end of the resistor to chassis. Try measuring the voltage at the junction of the 100k and the 10nF. The 10nF will remove most of the RF and your meter should then be able to read more accurately.

DMMs come in two varieties commonly. Ones with a 10M ohm input impedance, and those with 1M input impedance. If yours is a 10M input, the reading you see will be lower than the true value by about 1%, which is near enough not to worry about. With the 1M type, the reading will be about 9% lower than the true value.

The meter's manual should tell you which type you have. It if doesn't, it's easy to find out. Take a battery and measure the voltage with the meter directly. Measure the same voltage with the meter connected via a 100k resistor. If the readings two readings are within 1% of it's a 10M meter, if there is a 9% difference, its a 1M meter.

I don't know what the total power consumption is of the HW16, its PA has a maximum power input of 90W. I think you will be running close to the limit with a 200W transformer, it would be better to go for something a little larger. If you have too low a rated transformer, the voltage output will be lower than you expect and you'll be back to square one. Some transformers are not rated for continuous use at their maximum rating, they sometimes have specs like x watts maximum for y minutes, which is no use for your application.

Also be warned that some of the voltage converters on eBay are not transformers but switch mode power supplies. These are likely to generate a lot of interference and are not suitable for powering the HW16. A 200+VA mains transformer will weight several pounds and will be quite large, the switch mode type will be very compact and will be much lighter in weight.

A Google search for 300VA autotransformer should return something which is suitable for your needs.

Paula
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Old 14th May 2022, 2:24 pm   #9
Peterdee
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Default Re: Heathkit HG10-B VFO

Hi Paula
Thanks again for your post. I removed the 6CH8 valve so there should be no rf present? Did the same measurements again and got the same result 108v either side of R1. I did the test you mentioned with a 120kr and 9v battery.
without the R - 9.65v and with R in line 9.53v.
Although the voltage from the tx is low, 265v, I think it should be 300v I am still getting the correct 108v at pin 5 of the OB2.
Before I spend money on another transformer could I use the 150v with a resistor in line to bring it down to 120v? Also, could you give me details of the trick you mentioned of using a smaller transformer. I have a few salvaged transformers kicking around, so I may have something suitable.

Peter
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Old 14th May 2022, 4:06 pm   #10
frsimen
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Default Re: Heathkit HG10-B VFO

Hello Peter,

With the valve removed, there will be no oscillation and the only current drawn will be a few tens of microamps by the meter. You will measure 108V near enough on both sides of the resistor. All seems normal in that area from what you are reporting.

The purpose of the OB2 is to regulate the supply to the VFO to a constant 108V despite variations in the HT feeding it. 265V is on the low side but the OB2 is working properly. That low HT will be more of a problem in the HW16, particularly when combined with the unusually low heater voltage.

I'm a little concerned that the 110V output of your transformer may be as low as 100V, and that does beg the question as to what its power rating has.

Trying to drop from 150V to 120V with a resistor is not a good idea. The current drawn by the transmitter varies a lot between key down and key up. The 120V will be all over the place as a result if you use a resistor. The resistor would also be dissipating a lot of power, which is wasteful.

I've attached a diagram showing the general idea of the voltage booster. This goes between the step down transformer and the HW16. It uses a 230V to 24V mains transformer, which is running on the 110V supply, not the mains supply. If you do try this approach, make sure that the final item is kept in an enclosure to ensure that you can't get a shock from it.

Note that the if the 24V winding is connected the wrong way around, it will reduce rather than increase the output voltage, so you will need to check that you have the connection in the correct sense.

The output voltage from this arrangement will be much steadier with varying current than the dropping resistor approach.

Paula
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Old Yesterday, 8:51 am   #11
Peterdee
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Default Re: Heathkit HG10-B VFO

Hi again Paula
Thanks for your last post. Very informative and helpful as usual. I don't seem to have a 24v transformer. I have checked the output of the transformer and it is 110v from my 240v mains supply, I wonder if I could raise it to 120v it would make that much difference. What I am going to do next is go into the hw16 and see what the voltages are there, are they the same as the v's on the octagonal output. If not the problem could lie in the hw16.

PeterD
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