There is often background hash in valve radios and some comes in from the mains.

Delayed AGC / AVC tends to be more affected, however it does pay to check the AGC resistors. this is one area where resistors of 1/8 watt can often be used to get a close value to original.

If components have been changed in the RF section then you have no real option, if you want to do a proper job, other than to realign it.

There are procedures and stuffing too much signal down its throat is one of the biggest mistakes. We are talking micro volts. Too much signal will cause the AGC to operate and this is not at all desirable.

AGC voltage is hard to measure, in some cases & requires a high impedance meter.

Marc

I'd just disconnect the chassis mounted condensers and fit axial replacements underneath. It's much quicker and you get the original look above without having to dissect anything.

I'd just disconnect the chassis mounted condensers and fit axial replacements underneath. It's much quicker and you get the original look above without having to dissect anything.

This assumes that there's sufficient room under the chassis ... not always the case with small footprint chassis and can be a real problem when there's more than one multi-section cap involved -- a situation I have with some vintage interoffice intercoms.

The original power filter caps are 40μF Ducons. The nearest replacements I have found are 47μF 350v radials. Is that a reasonable replacement value?

Re-checking has confirmed that all the specified voltages are within spec already, so I don't think there is a serious current leak anywhere. It seems to be a matter of sensitivity, but I don't know where to locate the problem. A valve portable with a built-in loop antenna gets much better reception and hash suppression in the same environment.

Maven

350V sounds a bit low for filter electros. I'd be using at least 450 so there is lots of headroom - the higher rated condensers will definitely last longer. As for the capacity, I wouldn't go much higher than the rating otherwise it can stuff the rectifier valve. I must admit that I think 40μF sounds high. Most radios have 8 or 16μF electros.

The antenna system will affect what it will pick up: Inferior antenna, inferior performance.

A set that is miles out of alignment, will lack sensitivity and be fairly "deaf". Leaking coupling capacitors (plate to grid) feed positive to the grids. That impinges on the bias of the valves and adversely affects their behaviour: Grids do not like being positive.

I will see if I have the circuit? The voltage rating of the filters will be governed by the rectifier: Heater rectifiers do not generate the same surge as Silicon diodes & filament rectifiers like 80.

Marc

After looking at the circuit and data in AORSM’s that also contain alignment procedure: Voltages are quoted for a 1000 ohm per volt meter, which supports my comment re measurement of the AGC. They will not quote an AGC figure as that type of meter will load the circuit and be meaningless.

The B+ at the filament rectifier is 278V at the cathode to CT is 278V the set is back biased so the first filter cap is not grounded to chassis; It goes to CT. 350’s may be hard to get so get a better class of 450V. If space is tight consider RB rather than axial.

Did you check resistors as you changed the caps?

Marc

The antenna system will affect what it will pick up: Inferior antenna, inferior performance.

I've been reading up about antennae, having noticed that my Hotpoint 6 portable with internal loop antenna does much better than the Philips 179 with long wire.

This chassis is out of a 1955 radiogram, but I don't have the cabinet. Service docs don't mention antenna, but I'm wondering if this chassis is calibrated for a loop antenna. The chassis does have a paired antenna/ground socket, similar to the Hotpoint's loop antenna connection socket.

If a loop antenna inside the original cabinet was parallel to the antenna coil, then perhaps using a single-wire antenna messes up the alignment and antenna inductance.

Anyone seen that situation and have suggestion on making suitable loop antenna replacement ?

Re caps - I have got 2x 40μF 350v from JustRadios, where I also got the film replacements for the papers.

Maven

Just had a look at that circuit. Interesting to note the neutralising condenser formed by stator lug and stator contact on the band switch.

I've not seen that before, but then I haven't worked on a Philips radio either.

And the max reservoir capacitance for the 6V4 is stated as 50uF.

Hooked up this chassis to the loop antenna in the portable, and result was big improvement in signal level, reduction in background hash, though improvement is not evenly across the scale. I'll follow up with loop antenna options.

Alignment is still off, so I'll have to tackle that. AORSM instructions are comprehensible, but they assume professional experience or other documentation that I don't have. There's reference to a point 120 on a reference scale that doesn't appear on my dial or chassis.

The trimmers are above-chassis little cans having threads coming out the top with sharp pointed ends - no obvious tool purchase. Assuming I have to turn those to make alignment adjustments, what tool or technique should I use? Would a drop of penetrene be advisable before any twisting?

Maven

Kevin Chant has the Philips manufacturers service manual for the 179.

If the I.F. cans are those miniture Philips types, exercise some caution when adjusting, as they can be quite fragile.

To clarify - I'm not planning to touch the cores in any coils, only to adjust the trimming caps according to the service instructions (I got the manual from Kevin Chant's site). I'd appreciate advice on how to do that safely, as they don't have any heads on the adjusting screw shafts and I'm cautious to just attack them with a pair of pliers. None of the articles on alignment that I have found on the web describe this particular type of trimmer and how to adjust it.

Maven

Hi Maven,

The trimmers illustrated in the 179 service document seem to be the type known as beehive trimmers.

On this type of varible cap, there was an arrangement of faces spaced around the central pivot which looked like a hex or octal face which would mate with a minature nylon socket.

Every alignment pouch containing the common tools of the era would have a beehive socket. ( jaycal or rapar)?


Gheers, Graham...

I've taken a closer look with some magnification, and it looks like the trimmers work by twisting the top body of the cap, which raises or lowers the top section over the fixed bottom section, based on the fixed screw thread up the centre. If that's the case, it will just be a matter of breaking the wax seals and doing some careful twisting. Does that sound familiar to anybody?

Being a 3-band radio, there are six trimmers of this type. I don't know whether they have that "beehive" arrangement inside, but it looks more like a vertical adjustment system.

Maven

The Philips trimmers around 10mm in diameter have a triangle on the top from which the fixed screw protrudes.
Internally they are a labarinth, rather like a circular version of a tuning gang and are an air type as well

I actually have an adjustment tool for them. The top cap rotates to adjust. If there is doubt post photo.

Brass screws protruding from coils normally have a slot for a small screwdriver, some a flat tang. Unless the monkey has destroyed them. The AORSM has a drawing of which trimmer & padder is where. The aerial trimmers are set on the high end.

The 120 is for getting the dial cursor (pointer) in the right place before you mess with the rest. So with the tuning gang fully closed (low frequency end) there should be a 120 somewhere under or near the cursor.

Some sets like Kriesler & I think Breville had a set of calibration marks on the lower part of the dial, or backing plate for alignment purposes.

Adjusting a padder on the oscillator, which sets at abt. 600kHz (BC band) messes up the bandspread if you get it wrong and there is a warning as which screws you do not play with.

Marc