Bush DAC90 with U40 valves. Was such a set ever made?

[FERNSEH]

Did Bush Radio make a version of the DAC90 equipped with U40 0.1amp B8A base valves? Essentially an interim model between the DAC90 with octal valves and the DAC90A with U40 valves and a completely different chassis metalwork design.
Adaptor plates would be fitted for the smaller B8A valve bases in the 1-1/8" holes for octal valve bases.

DFWB.

[bobhowe]

HI David Adapter plates proper project .What number is the U40 valves as i Googled U40 Valve and the search results i got were gas meters kind regards Bob

[ms660]

U series Rimlock, eg: UCH42, UF41 etc.

Lawrence.

[bobhowe]

Thanks Lawrence kind regards Bob

[bobhowe]

Hi David are you going to do the Bob Howe UL44 Valve conversion ? . If you use a UCH81 instead of UCH42 apart from increasing the heater volts by 5 volts and use a B9A valve base is there any other changes ? & is it going to be an Autotransformer that you are are going to ask Ed Dinning to wind kind regards Bob

[FERNSEH]

"Hi David are you going to do the Bob Howe UL44 Valve conversion?"
Hi Bob,
sure will, and for the frequency changer the superior UCH81. I don't expect any problems with the later valve.
The three other valves will be the UF41, UBC41 and UY41.
Replace the mains dropper with Ed's mains transformer.

DFWB.

[turretslug]

I suppose there's also a possible 0.1A Loktal (B8B) conversion option for the DAC90, keeping a "big bottle" look....

[bobhowe]

Hi David great you are going to do my UL44 conversion . Is there any other changes in using the UCH81 apart from increasing the heater volts by 5 volts and changing the valve base and connections kind regards Bob

[FERNSEH]

turretslug wrote: "I suppose there's also a possible 0.1A Loktal (B8B) conversion option for the DAC90, keeping a "big bottle" look...."
The Philips or Mullard UCH21, UCH21, UBL21 and UY21 valve line-up could be considered but will involve extensive modifications to the under chassis wiring.
An RF/IF amplifier pentode type UF21 was made but is a very rare valve.
An UBC21 was never made.

DFWB.

[Herald1360]

There would be a spare hole in the chassis with that lineup. Add another UBL21 for some added P-P oomph? And even less dropper resistor dissipation

[FERNSEH]

"There would be a spare hole in the chassis with that lineup. Add another UBL21 for some added P-P oomph? And even less dropper resistor dissipation"
But then there would be a requirement for a phase splitter for the two output valves.
The attachment shows the circuit of an AC/DC amplifier which employs 0.2amp valves. A CCH35 triode-hexode is pressed into service as the phase splitter.
Circuit was found in the 1949 Mullard Maintenance Manual.

DFWB.

[Herald1360]

Rats! Get rid of the UY21, add another UCH21 and sneak in a selenium rectifier

[ms660]

Originally Posted by FERNSEH

The attachment shows the circuit of an AC/DC amplifier which employs 0.2amp valves. A CCH35 triode-hexode is pressed into service as the phase splitter.
Circuit was found in the 1949 Mullard Maintenance Manual.

Those EL33's will struggle, not to mention the others....

Here's the same schematic from a 1951 manual using U series valves (manual page 238):

https://frank.pocnet.net/other/Mulla...anual-1951.pdf

Lawrence.

[bobhowe]

Hi David going to take your advise about using a UCH81 for the frequency changer instead of the UCH42 what other modifications do you need to do apart from changing valve base & increase the heater voltage by 5 volts kind regards Bob

[FERNSEH]

Performance wise the UCH81 and the ECH81 can be regarded as the best frequency changer valve of all.

DFWB.

[bobhowe]

Hi David looking forward to see a substitution diagram for the UCH81 in a DAC90A kind regards Bob

[FERNSEH]

Hi Bob,
to be honest after looking at the Mullard information for the UCH42 and UCH81 there is very little difference in the performance of the two valves.
At 170 volts the conversion conductance of the UCH42 is 670uA/V and the UCH81 is 750uA/V.
Nevertheless, it might be an interesting experiment to find out how the later valve performs in the DAC90A.
In the UCH81 the oscillator injection grid is brought out to a separate pin so it will be necessary to connect pins 7 and 9 together.
Actually, in terms of performance the older CCH35 isn't all that far behind to two later frequency changer valves. 650uA/V @ Va 250V.

DFWB.

[mister valve]

Originally Posted by ms660

Those EL33's will struggle, not to mention the others....

Here's the same schematic from a 1951 manual using U series valves (manual page 238):

https://frank.pocnet.net/other/Mulla...anual-1951.pdf

Lawrence.

I think the EL33 valves as listed, is a misprint. I'm certain it should be CL33 valves as they are 200mA heaters like all the others in the heater chain.

[ms660]

Originally Posted by mister valve

I think the EL33 valves as listed, is a misprint. I'm certain it should be CL33 valves as they are 200mA heaters like all the others in the heater chain.

Yes, that was the point of my post.

Lawrence.

[bobhowe]

Thanks David i will give it a try when the Valve arrives kind regards Bob