This large table top radio was an export model to Aust. and NZ 1936/7. I have a circuit only. Would appreciate any tech. and align info if anyone has. Valves; 80 42 6D6 (2) 6A7 6B7.

Would be interesting to see the circuit to detirmine if it has AGC / AVC, With those valves it is likely.

Normally IF frequency is on the circuit? If so that makes things easier. It may have air trimmers?

A little more info on that side, perhaps a photo of the chassis.

Marc

Have forwarded some photos and circuit for your comments.

Tim.

At the time of writing no circuit. The photos show paper caps and they need to be rid of, providing that you have not re-stuffed the old jacket with a new one?

The "Dry" Electrolytic is also a candidate for re-stuffing. I note the two filter caps on the speaker, they did that on 661 from memory. I actually used two tag strips & strung the new ones between them. I have suspicion that it was back biased?

I note that the cans are the same deal as EMMCO & they may have made them? Those are actually bottom trimmers like the EMMCO Troubador I fixed. Do not adjust them without equipment, or the set sideways.

I note the globes carrying two wires, that may indicate that the 6.3V heater rail is on a centre tapped winding and the valve pins must not be earthed to chassis.

Also make sure there is good insulation paper between the live wires on the transformer & the bell. There is an earthwire on the transformer, that says shielded transformer, so I would like to see an earthed cable, to bleed of the charge it will put on it.

Looks like a fairly typical HMV and not overly complex.

Await circuit.

Marc

The Australian version of the 471 is the 718. Same cabinet, same valve line-up, but minus the long-wave band.

http://trove.nla.gov.au/ndp/del/article/86048867

http://www.kevinchant.com/uploads/7/1/0/8/7108231/718719720.pdf

Thanks Marc and Monochrome. All paper and electro's have been re-stuffed or replaced. A few resistors too far out also. One side of 6.3 volt winding is earthed. The set is working but lacks sensitivity as yet. I wanted to see what the IF frequency was before proceeding further.

The 718 circuit is similar but with a simpler tone circuit. It also has the tapped vol. control.

The 718 appears to use the same coil assemblies as the 471, and has an IF of 460kHz, so I'm assuming the 471 is the same. The parent UK set had an IF of 125kHz just to confuse things.

Tim.

I would expect that after the mid thirties the IF's would have standardised around 455kHz albeit that HMV did go to an odd frequency. That did make sense as the idea was to to not have a Hetrodyne on the frequency of a radio station.

The question now is what do you have to align it? HMV is one manufacturer that recommends re-calibration of the RF section after changing parts: I always do it.

The biggest cause of "Deaf" sets is calibration and fault finding is a waste of time, until it is re-set.

I normally set the aerial coils with the set in its running configuration. I.e. If it needs an antenna, its fitted. The antenna trimmers are peaked at around 1500kHz (BC) on a weak signal. When fitted,oscillator padders (first) on BC 600kHz.

Marc

I have sent the circuit diagram but it hasn't appeared yet. as far as calibration goes. I have sig.generators from Heathkit, Avo, Hickok and Windsor 66 a which I use most. critical frequencies have been checked with a frequency counter.

The circuit does have a few unusual features which can be seen in the 718 also.

HMV 471 Circuit Diagram

The critical thing when doing an IF alignment, is to not cram too much signal into the Pentagrid. You only need around 40uV. Too much signal will activate the AGC and then you will never get it right. Always use a series cap between generator & Pentagrid (6A7 Top Cap).

I use a frequency counter to set the Generator. I do a few radio's so have a box with the attenuator's in it and it is a permanent setup where the Counter, Generator and a CRO are coupled to it via dedicated cables.

Do not calibrate the Generator with its modulation / tone on.

Marc

Circuit diagram uploaded.