I am trying to align my Music Masters 5 valve 1941 vintage radio. It has MW and SW.

When it first ran it was OK but it howled and squealed between stations and to some degree on the station. I don't have a schematic for this chassis but other MM radios used the standard 455kHz so I aligned it to that. The squealing continued so I changed the 6U7G valve and it became more stable and the squealing stopped. It picks up stations ok but not great so I tried adjusting it by ear to see if it improved which it did but then decided to set it to 455 again.

My issue is when I align it to 455 I also get peaks (generator tone) at about 425, 500 and 525 kHz as I move the signal generator through the scale. The tone at 525 is much louder. Those number are rough as the SG scale is a little out and I normally use an oscilloscope to check the SG frequency.

I am just laying the SG cable across a short wire coil attached to the aerial on the radio and the SG earth connected to chassis. The tuning condenser is fully open or closed, makes no difference, the radio volume is on max and the SG tone is on the lowest volume. The tuning screws seem to be a fair way away from their original positions. The radio works with strong stations coming in loud and clear, weaker stations have a fair bit of hash behind them which is normal here.

Does that mean 455kHz may not be correct or should I be content with what I have?

The valve line up is 5Y3GT, 6V6GT, 6U7G, 6B6G and EK2G.

Thanks

That could be wartime production with EK2G. Left without a shield 6U7 will go berserk and rarely doesn't. If it is oscillating you will never tune it.

If your signal generator is off frequency you have a problem. Make sure EK2G / EK32 has not got a break in the metalisation at the base? If the base is loose it is liable to be broken. Metalisation is its shield and is connected to a grounded pin 1 (Octal).

I would suggest coupling to the TC of the Octode with say 200pF in series. To much signal input (over abt 50uV) will activate the AGC where fitted, then you will not get the IF right.

Most of the IFT's have a slug at the top and bottom, some sides, & then there are top & bottom tuners with trimmers. Beware with the latter one will be live & they do not appreciate being shorted.

If you set the Generator with a Frequency Counter? Modulation / Tone must be off.

There might be a circuit on Kevin Chant site? Most of those seem to be 455kHz

I have no data on it. Make sure that there are still no oscillation issues etc. before attempting a retune.

Do not turn 5Y3 sideways.

Tippy, having odd multiple peaks rings a bell. One of my projects where I used threaded core adjustor IF's did that and showed an odd bandpass curve. I cant quite remember which project it was in, but the cure was to do with "inner and outer peak". Because the cores are long enough in relation to the coil winding width you can resonate each coil at the chosen frequency either going into, or, coming out of the coil, hope you see what I mean. Thus you can peak the transformer with the cores either "outer" "inner" or a mixture of positions!
The COUPLING between the primary and secondary and the response curve is very different when tested as 2 x "outer" or 2 x
'inner" positions. Each IF type is going to be different so I would explore what happens if you shift from one position to the other.
My multiple peaks and odd curve dissapered when I used the "right" position.
Fred.

Thanks Marcc, 6U7 has an earthed shield and the EK2G Metalisation is intact and earthed to the chassis. It's 1941 so yes, war production. I will try connecting the SG to the top cap as well. My SG is just slightly off the analogue scale markings so I set it with an oscilloscope to be sure, Is that ok? Thanks for the reminder with the 5YG and it's tendency to short

Thanks Fred, that's a good point, I will experiment and see if it will make a difference

Do you disable the sets oscillator when you are doing the alignment?

Hi Nhanwell, errr... what? disable the oscillator? I can safely say no, should I? and why should I? and how do I?

I'm all ears

Some sets where the exciter is separate do disable the oscillator, but rarely do other sets do that. Often where there is a padder the oscillator is set at around 600kHz, second. The mechanical alignment of the dial is first.

I never calibrate frequency with the Oscilloscopes here, I built a counter in the 70's, Albeit that the Generator has provision for Heterodyning against a crystal, of which I have a few: One being 455kHz. That's not much use with many HMV sets.

Because of set volume I built a "Black Box" that couples the generator audio to a CRO sync and the counter to the OP of the Generator plus has the Attenuators to reduce the signal & block DC. DC blocking is important as some Generators have potentiometers as attenuators & these wipe out the signal grid bias. These Generators also put out Volts & one only needs micro volts.

As noted: I use a CRO to monitor the OP when calibrating. It is much more sensitive & stable, especially when synchronised with the Generator. It also spots distortion & then can be used to find the source point. This setup is virtually permanent on a shelf above the action and saves on having wires everywhere & wasting time setting up frequently: All of the coupling wires, including audio, are shielded, Box is metal.

There are a lot of multiples in the mixer. The object is to only let 455kHz through & attenuate the rest. One must be careful that the 455kHz is from (in most cases) the oscillator running 455kHz above the incoming signal & not below it.

Alignment has many traps.

The signal generator can be rough checked against a radio station as you get , 2nd, 3rd, harmonics, 455, 910 1365 only stations like WWV & WWVH are guaranteed to be spot on. & the mechanical dials on some Generators are not that good for either band spread, or accuracy & coils change over time.

Also watch lead dress. Wires above the chassis can induct & shielding & part location especially in and around the second detector, first audio. I have often had to add shielded wire there.

Sounds like an ideal setup Marc, I was thinking of using a CRO (digital one though) to check the OP, you have inspired me to give it a go. I can also read the frequency of the SG at the same time.

I've taken your other tips onboard as well, Thanks

I know its a bit of information overload but you might look at the SC micromite IF alinement kit.
This basically is a sweep generator with a screen readout and is a very handy device. The inherent calibration/accuracy of the unit agrees with my frequency counters and gives you another generator/measuring tool to augment and cross check your exisiting metering.
I immediately used it to sweep both IF and RF tuned circuits for response and ditched my valve sweep generator there and then!
Its a kit you have to stick together with little teeny tiny bits but if I can do you with fading eyes and shaky hands you should walk it in!

I posted a couple of comments on the kit in the special projects section.
Fred.

That looks pretty good, I read your article and have ordered one. Father's day is just round the corner too, thanks Fred.

Just beware with modern equipment with Valve radios, a lot of it won't handle RF well, nor the voltage. One of the reasons you see caps around 1KV Plates 250VDC is the transients in the audio. The plate bypass was one of the most common ones to fail in many old sets.

Yeah, good point Marc, Thanks

QUOTE: The COUPLING between the primary and secondary and the response curve is very different when tested as 2 x "outer" or 2 x 'inner" positions. Each IF type is going to be different so I would explore what happens if you shift from one position to the other. My multiple peaks and odd curve dissapered when I used the "right" position.

If the coupling becomes too tight, you can get a pair of peaks, one above and one below the desired frequency. This can sometimes be used to your advantage, if you can adjust things so you get a reasonably flat response +- 9kHz around the radio station's carrier, so the detected audio doesn't have the high audio frequencies reduced. To get "hifi" AM reception for local AM stations. At the cost of getting "monkey chatter" from distant out of town stations.

To actually see it, you'd need a setup like this, at my web page
about 3/5 the way down this page
"A setup to look at passbands of filters"

Fred's recommendation of the Silicon Chip Micromite sweep generator is spot on. This is an excellent device, you can get exactly the response you need quickly and accurately.

http://www.siliconchip.com.au/Issue/2017/September/Dead+simple+radio+IF+alignment+with+DDS?res=nonflash

Here's Fred's post about it:

https://vintage-radio.com.au/default.asp?f=12&th=56

Get one!

Hi Wa2ise, thanks, sounds interesting, I will investigate further.

As suggested, I ordered a Micromite IF kit from SC and assembled it. I plugged in the backpack part without the DDS module to test it as is suggested in the SC article but it doesn't display anything. The backlight works but no graphics are displayed. I checked everything but can't see any errors. I have emailed the SC tech dept and will see what happens. I can't imagine I've done anything wrong as there are only about 10 components to fit.

I wonder if the chip has been programmed. I purchased the correct kit BTY, with the software preloaded.