Convert Bush DAC90 or AC91 to battery use.

[FERNSEH]

Yesterday the Bush radio was equipped with batteries. From Lidl's ten 6F22 (PP3) and one R20 cell.
Results were disappointing, terrible instability and with the usual ten feet of wire as the aerial only the strongest local stations coming through. Fitting a 16mfd capacitor between HT and chassis improved matters considerably, that part should have fitted during the construction of this chassis.
However, it turns out the set needs an earth connection, without the performance is just so-so.
Connect some sort of earth connection and the set really comes to life.
The three waveband coil pack came from a Bush SUG3. I have a Bush SUG3 upstairs. It'll be interesting to find out if that set has the same characteristics i.e. needs an earth connection.

DFWB.

[bobhowe]

Hi David glad that set is working would the Bush SUG3 Have an earth socket on the back ? just looked on the back of my Bush AC91 & there is an earth socket on the back kind regards Bob

[FERNSEH]

Hi Bob, the SUG3 has aerial and earth sockets.
Topic about my SUG3. Nothing about the performance of the set, just my solution to stop the set falling over.
https://www.vintage-radio.net/forum/...d.php?t=144593

DFWB.

[bobhowe]

H David seen the SUG3 thread bet they work well with the big speaker in it kind regards Bob

[bobhowe]

Hi David please can you post some pictures of the HT battery in its final form of eleven PP3s kind regards Bob

[FERNSEH]

Hi Bob,
will certainly do that. The DL41 can operate with an anode voltage of 120V and as there is just enough space for eleven PP3 batteries so why not supply the set with 99volts? Output is 330mW with 90volts. 550mW with 120V.
With regards to the output valve a degree of battery economy can be realised by using only half of the filament. With the DL41 pin 7 can be disconnected leaving only section of the filament active. If = 50mA.
But things aren't so easy, the optimum with both filament sections is 11.3Kohms with a plate voltage of 90V. When only one filament section is in use the load becomes 22.5Kohms with 90V.
A special output transformer is required with turns ratios of 85:1 and 60:1.
Were any portable radios ever made which had an economy switch?

DFWB.

[Ed_Dinning]

Him David, I think I recall a circuit that had such a switch, but not on a Bush set.
I'm equally certain there was not a tapped output transformers so no change of load

Ed

[ms660]

Philips LD562AB...Economy switch:

http://www.georg-knoechel.de/radio-s...ld562ab-sp.jpg

Lawrence.

[kalee20]

Originally Posted by FERNSEH

Were any portable radios ever made which had an economy switch?.

Yes.

Vidor Vanguard (DL96) had such a switch, it cut half the filament.

And Ever Ready Sky Emperor, push-pull DL96's.

The business of rejigging the OP transformer was not carried out in either, so with half the filament, half the anode current, same anode load, available output power would be reduced to a quarter (rather than half).

But certainly the Sky Emperor went to town on the switching, as AM, FM, and Gram input, the unused valves were switched off, causing 3 different possible HT currents. So each mode required a different value of back-bias resistor to give the same grid bias for the DL96's, which obviously had to be switched in. Then add the economy mode, and you double-up on these three resistors.

Horrendous!

[FERNSEH]

Originally Posted by Ed_Dinning

Hi David, I think I recall a circuit that had such a switch, but not on a Bush set.
I'm equally certain there was not a tapped output transformers so no change of load

Ed

Hi Ed,
doesn't seem any manufacturer bothered to alter the anode load of the output valve(s). Probably used the economy switch as a sales gimmick.

DFWB.

[G.Castle]

Originally Posted by kalee20

Yes.

Vidor Vanguard (DL96) had such a switch, it cut half the filament.

Hi all.

On the subject of the economy switch, in the Vidor Vanguard CN436 as built S14, is the economy switch, its operated by a push pull movement on the tuning drive spindle. When opened, it inserts R30 (2k7) into the HT feed and reduces the HT line voltage.

That having been said, an example of the set that is in my care, does have S14 so that disconnects one side of the filament in the output valve: the valve is not the specified DL96, but a Russian rod pentode type 1j29b. Obviously a modification in this case.

Greg.

[kalee20]

I do have a Vanguard myself (it's untouched, unexplored, wrapped up among the round tuit pile) and I know of the push-pull economy switch, I’m just not yet familiar enough to know how it did it.

Cutting filament power being a credible modus operandi (seeing as Ever Ready did it in the Sky Emperor), I drew the unjustified conclusion Vidor used it as-built in the Vanguard. I have just looked at the circuit and see it isn’t the case, there's the crude resistor introduced, exactly as Greg says.

The idea of just dropping the voltage by resistor in HT+ is horrid, especially to the oscillator… Though, so is power-down of half the filament. Just imagine, after significant use in economy mode, one ends up with a DL96 which is half-used, half-new!

[FERNSEH]

Many thanks to Bob Howe for the kind donation of a three waveband dial glass.
The yellow box contains ten PP3 batteries. For the HT a replica of the Ever-Ready B117 will be made and LT will be supplied by two parallel connected R20 cells.

DFWB.

[bobhowe]

Hi David glad i could help set looking great next thing is the back and should it be called DFWB 90B on the back kind regards Bob

[FERNSEH]

Hi Bob,
I happened to find a DAC90 back in the shop today. Needs a patch where the mains dropper did the usual heat damage. No heat problems with the DFWB90B.

DFWB.

[bobhowe]

Hi David great you have found a back DFWB 90B will look good when finished kind regards Bob

[FERNSEH]

A mains power supply unit will be constructed for the Battery Bush radio.
An Eddystone diecast box with the dimensions of 120 X 97 X 57mm will be a perfect size to fit in the space allocated for the HT battery.
A mains transformer made by a firm called Isoplethics was made specifically for battery receivers. The HT supply is the easy part of the power supplier construction but special care must be taken to ensure the filament supply doesn't exceed 1.5volts. 1.4 is the ideal filament voltage.
Being close to the power unit box the DAF91 valve looks rather vulnerable.
The valveholder will be replaced with one with a skirt and screening can.

DFWB.

[FERNSEH]

Tested the mains transformer today.
The primary has a resistance of 879ohms. The 100volt HT winding is 473ohms and the 70 volt tap is 318ohms.
The resistance of the 3.5volt winding is 1.1ohms and the 7.5volt winding is 25ohms.
With 244volt mains input the 100volt winding delivers 139volts and the 70 volt tap 96V.
The 3.5 and 7.5volt windings deliver 5volts and 10volts.
All these voltages were measured off-load.

DFWB.