I've recently been asked about a Pye TV tuner which has a problem. The problem was described as being "seems to be a fault inside which results in most of the channels being right on the edge of the fine tuning range".

This does indeed indicate that the tuner is in need of adjustment but should only be undertaken when it it really necessary. Once you start to alter the settings there is no easy way back and it should only be attempted if you are confident of your skills.

Pye TV's of the 1960's generally used an incremental inductance type which used switches to progressively alter the inductances in the tuned circuits within the tuner. This is quite different from many other tuners in use at the time of the turret type that physically moved complete "biscuits" of tuned circuits into use.

The incremental tuners can and will gradually drift out of calibration due to age and component deterioration and also valve replacement. They are particularly sensitive to this problem as they rely on the addition of multiple coils for the tuning of the low number channels where as the higher channels are only using a few.

To get these tuners working on the correct range of the the fine tuning control requires adjustment of the main local oscillator coil. NOTE: This adjustment will affect every channel setting. The other channels will need to be individually adjusted in sequence if needed to correct their tuning range.

The following procedure is for the Pye EAF-207 and Pye EAF-236 tuners as used in some models of the Pye Pedigree 501P model series sets. Many different tuners and chassis variations were used so these notes will not necessarily apply to all models.

The tuner needs to be set to the highest channel that can be received (Channel 10 is most likely) and the fine tuning control set to the middle of its range. Then carefully remove the the channel selector and fine tuning knobs (they should pull off).
Visible through the hole should be the front of the tuner with a small circular hole on one side of the tuner shaft with a much larger cutout near the circular hole. The small hole gives access to the Ch 11 Local Oscillator coil adjustment. As mentioned earlier this is the PRIMARY adjustment point for the tuner and affects ALL channels. With the set turned on this coil is adjusted with an insulated tool. An old plastic knitting needle with a wedge sharpened at one end is ideal. DO NOT use metallic adjusters - they will change the tuning by being near the tuner so adjustment cannot be easily done aside from the dangers of high voltages in the tuner.

Quoting from the service notes do the adjustment as follows " Using an insulated trimming tool, turn the channel eleven oscillator coil screw anti-clockwise if the picture is excessively broken with sound, or clockwise, if the picture definition is poor, until it is on the point of being broken with sound."

With the Ch 11 coil set it is probable that the remaining channels have now fallen back into their correct adjustment range within the fine tuning range. If not then each individual channel will need to be adjusted starting from the highest channels and working down towards channel 0. These adjustments are accessible through the larger opening and are adjusted in one of three ways depending on which channels are being adjusted.
These adjustments generally consist of bending small and delicate wires or coils and so it is not recommended that they are disturbed unless absolutely necessary. If anyone wants me to go into the details of these adjustments I will but I will need more information on the particular tuner fitted as there are wide differences in procedures.

Andrew

Thanks, Andrew. My Pedigree's got a turret tuner, but on the basis of your advice I might try replacing the oscillator valve and see if there's an improvement. If not, it's easy to put the old one back!

Yours is a later model than I thought. Pye's are very difficult to identify without both their model numbers and chassis numbers due to the many variations made.

Since you have a turret type tuner then I would recommend looking at simple faults first before trying to adjust the tuner. These are normally set up on the bench and it is strongly discouraged that any adjustments are made in the field.

Trying a different mixer/oscillator valve is well worthwhile as this can cause the unit to go out of correct tune.

With analogue transmissions about to cease having the tuner off frequency may not be much of a problem as long as your RF modulator can be adjusted to a frequency the TV likes.

If you still want to have a go at adjusting your tuner, we'll need to identify the exact type you have so that I can see if I have the correct information for your particular model.

Andrew

I'll be OK even if can't adjust the tuner because as it is it can just receive 5A. But it would be useful to know how to do the adjustment. The set is a 501PA, and the chassis number is T23-14D. It's the "hybrid", semi-transistorised version of the set. The tuner has a string of numbers on it: 4032 103 62, and 2 12 68. The tuner valves are 6GK5 and 6HG8. I've got a circuit diagram of the set's chassis that was published in Electronics Australia (Dec 66), but they didn't bother to show the circuit of the tuner.

Hi Sue, I've done some research and I think I have an answer for your problem.

I've identified your tuner. It is actually an Astor made tuner with the part number 4052 103 62 (confirmed on parts lists I have) and 2 12 68 would be a manufacturing date.

The T23 chassis manual does not contain any detail on the tuner aside from a drawing of it and its Pye part number.

I've cross checked with the Astor manuals and they do not detail their tuners either and refer only to specific service bulletins for the various tuners. I don't have many of these bulletins so I don't have the actual circuit.

However, all tuners based on the 6GK5 and 6HG8 are pretty much the same and checking with some other manufactures manuals shows that their is usually no master oscillator adjustment. The fine tuning should cover a very wide range and account for any changes in valves etc.

This along with the Pye drawing of your tuner makes me suspect you have a mechanical problem with your tuner. The drawing shows your tuner is a standard late model with gears driving little tuning slugs on the individual turret wafers. These type of fine tuning mechanisms normally have a range of many turns of the control. In an earlier post I think you said you only had an adjustment range of half a turn.

I've recently had a similar problem with a Thorn tuner where the fine tuning control would turn a small amount but was actually seized. The cure was to dismantle the fine tuning control mechanism and regrease the area where the main plastic part of the mechanism rotates on the fine tuning control shaft. This is normally a friction drive and should turn after overcoming a small amount of resistance.

Hopefully this will be the answer for your problem. If you get stuck when trying to figure out the problem with the mechanism, I'll try and explain it better.

Andrew

Thanks Andrew. I've had a look inside the tuner, and I can see the tuning slugs moving up and down properly as I turn the fine tuning. So the problem's elsewhere. I'll try a different valve next, just in case. I've noticed the supply line to the tuner is at 150V when it should be 130V. There's nothing wrong with the power supply or the dropping resistors, so this suggests there's something wrong electrically inside the tuner.

Hmm, we're eliminating the simple things one by one. If another valve doesn't solve the problem then I agree the tuner is probably faulty.

Try another valve as that is the most likely cause left for the problem. If that doesn't help, I'll dig out a circuit that's similar to your tuner and arrange to get a copy too you.

TV Collector, if you e-mail the image of the circuit to me I can include it in your post.

I've emailed Brad a scan of an AWA model TB10 tuner circuit from around the 1968 era. This tuner will be similar to that used by Astor/Pye but not identical.

Click on image for larger resolution

I've now tried two other 6HG8 valves in the tuner; one made no difference, and the other just made the mis-tuning worse.

Thanks for the circuit. The layout of the tuner looks similar, with the three trimmers on top. I guess I'll have a look inside mine at some stage, and service it my usual way, which is to replace everything possible in the suspect area with new components!

Well that seems to settle the question then.

I'm still concerned about you only having half a turn of fine tuning adjustment. Your tuner should have at least two or three full turns of adjustment. Can you confirm that you only get half of a turn adjustment?

A fault in the tuner is quite possible after all these years and so you may need to dive in but unless you have the necessary alignment equipment any changes you make inside the tuner will likely degrade its performance. The position of components and lead lengths is fairly critical and needs to be duplicated when parts are replaced.

I'd suspect resistors as being the most likely to blame. The ceramic capacitors are normally reliable.

No, the fine tuning rotates through several turns. I meant that I'd expect the tuning to be right at half the maximum turns.

You're right, I don't have the gear or the expertise to properly adjust a tuner, so I'm wary about changing anything. All I've done is made a few tests with a multimeter. The 10k oscillator grid resistor's gone up to 15k. That'd upset the bias, wouldn't it?

By the way, the oscillator circuit is slightly different from the AWA one you posted, from what I can see. (Which isn't a lot, without taking the tuner out.)

That makes things a bit clearer for me.

The 10k resistor would certainly not help by drifting to 15k. I can't say what the effect would be but it won't be helpful.

Unfortunately the AWA circuit is the closest I have at the moment and was really meant as a guide to the general design of the tuner. There will be detail differences. Until I can track down the elusive Astor service bulletins, I can only go on what little information I have.

I have an Astor tuner here that I've compared to the AWA circuit and it is generally similar. I did notice though that R5 (2k2) in the AWA tuner was a much higher value in the Astor. I think it was around 47k (I'd need to recheck to confirm).

Best thing to do would be to remove the tuner and partly dismantle it and check the resistor values. You can remove the turret assembly without affecting the alignment. Just make sure you don't move any parts and all should be fine.

OK, I'll give it a go. I'll try to draw a circuit diagram while I'm at it.

Hi Sue

I know it's an old post, but in a past life I used to fix heaps of these Astor tuners.

Remove the FT mech and the turret. On the 6HG8 socket you'll find a 4.7k 1w resistor. On the same pin is a 22pf ceramic capacitor. Our standard fix was to replace the cap with a 22pf NPO and the 4.7k resistor with a 1.5w 5.6k carbon film resistor. The cap change fixed local oscillator thermal drift and the resistor change helped the life of the 6HG8. The 4.7k had usually gone low in resistance and you can see clear signs of it overheating.

That, and cracked solder joints around the metalwork that holds the stationary contact assembly, and a good clean using silver polish followed by a smear of CRC was about all that ever went wrong with those tuners.