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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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20th Feb 2014, 4:40 pm | #1 |
Pentode
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Why all those taps on 1920s H.T. batteries?
Some time ago. I had wondered why these H.T. batteries on your side of the Atlantic have so many voltage taps. From my experience when operating 1920s radios, I do not recall ever needing H.T. voltage taps of more than 22, 45, 60, 90, 135 Volts. I just seems like much too much labor and materials to provide all these taps.
The only thing that comes to mind is that the batteries with many voltage taps can be considered as a combination 'B' and 'C' battery. I think at some point they realized this as a false economy since the cells being used for 'C' bias will experience almost no current drain. Those cells will be almost new when the rest of the battery is exhausted. Comments welcome.. Robert |
20th Feb 2014, 5:41 pm | #2 |
Dekatron
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Re: Why all those taps on 1920s H.T. batteries?
Hi,
I'd always assumed that it was as the battery ran down, the plug would be moved up a tap to maintain the correct HT voltage. I'm probably wrong though. Cheers, Pete.
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20th Feb 2014, 5:44 pm | #3 |
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Re: Why all those taps on 1920s H.T. batteries?
Some battery radios don't have screen grid dropper resistors and derive the screen grid voltage from the taps.
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20th Feb 2014, 5:45 pm | #4 |
Dekatron
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Re: Why all those taps on 1920s H.T. batteries?
Getting early receivers to approach the point of optimum reaction was tricky - selecting the correct HT voltage (and screen-grid voltage in the case of tetrodes) was tricky. You adjusted the battery tapping to find the 'sweet spot'.
Similarly, tap-swapping to adjust the screen-grid voltage on a tetrode provided a primitive form of gain-contr=ol. |
20th Feb 2014, 6:36 pm | #5 |
Nonode
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Re: Why all those taps on 1920s H.T. batteries?
I can't see how some of those voltages are achievable with 1.5v cells?
David
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20th Feb 2014, 7:06 pm | #6 |
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Re: Why all those taps on 1920s H.T. batteries?
Some radios had direct separate connection for the anode and screen supplies. Usually the detector would have a much lower voltage and the output valve the maximum battery voltage. Screen grid valves used an intermediate voltage. Direct connection to the battery would also remove the need for decoupling. It is likely that because the batteries were consumable items a single general purpose type might have been economical.
I wonder whether the cost of the extra tappings was significant. I am sure that the batteries were hand soldered anyway and the taps were only a short piece of brass tube. I have somewhere a battery eliminator with three output connectors one marked HT+ one screen grid and I think the other is marked Det. This suggests the separate connections was common on battery radios. |
20th Feb 2014, 11:12 pm | #7 |
Dekatron
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Re: Why all those taps on 1920s H.T. batteries?
Most battery elimanators had at least three taps including "Screen Grid".
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21st Feb 2014, 12:57 am | #8 |
Dekatron
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Re: Why all those taps on 1920s H.T. batteries?
No, but at some point in the battery life the socket would probably have that voltage on it for a while
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21st Feb 2014, 1:25 am | #9 |
Nonode
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Re: Why all those taps on 1920s H.T. batteries?
Does that battery use the mathematical symbol for division to denote the negative terminal?
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21st Feb 2014, 9:48 am | #10 |
Dekatron
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Re: Why all those taps on 1920s H.T. batteries?
I have never seen a radio battery with so many taps! I think it would have been purchased in the 1920's by todays version of the typical Hacker/Roberts/Dynatron customer. It was never that critical, most receivers having 120V H.T. for the output pentode and around 60V for the detector. They may have thought back in the 1920's, the more wires in the wireless, the better! John.
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21st Feb 2014, 9:54 am | #11 |
Rest in Peace
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Re: Why all those taps on 1920s H.T. batteries?
Related to the above, I recall my father saying that early radios had a 'Grid Bias' battery, which, IIRC, was 9 volts. The standard HT (B+) was 120v, whilst valve filaments (heaters0 were run from a 2v accumulator. Those tappings could have been, as suggested, for seperate anode & screen grid supplies, although what all the different voltages on the battery in post#1 were for I know not!
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21st Feb 2014, 10:32 am | #12 |
Nonode
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Re: Why all those taps on 1920s H.T. batteries?
I was told, perhaps wrongly, that HT batteries with numerous voltage tappings were largely for testing, experimental or lab use, not for everyday use in domestic sets.
There were after all also a lot of batteries with only a single output voltage. In the case of a home built or modified set a multi voltage battery would be useful initialy, but once it was found that say 90 volts HT was optimum then it would make more sense to buy a staight 90 volt battery. Another possibility would be batteries for export to remote places. The general store somwhere very remote, and weeks away by steamship, might reasonably keep in stock a few multivoltage batteries suitable for numerous applications. They could probably not keep even 2 of each of numerous different types of battery, apart from the shelf space and capital tied up, the batteries would probably spoil before being sold, especialy in tropical conditions. |
21st Feb 2014, 11:18 am | #13 | |
Nonode
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Re: Why all those taps on 1920s H.T. batteries?
Quote:
I've just had a look inside one of my radios and it needs 3 H.T. and 2 G.B. voltages. The voltages required for the H.T. also varies depending on the chosen valve lineup. David
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21st Feb 2014, 2:14 pm | #14 |
Dekatron
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Re: Why all those taps on 1920s H.T. batteries?
Was it definitely a radio battery? So many taps and only up to 90V seems odd.
Also, it appears to go from 3 to 90, with no suggestion of negative voltages for GB (although it could be arranged, but not obviously to most owners) |
21st Feb 2014, 9:45 pm | #15 |
Hexode
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Re: Why all those taps on 1920s H.T. batteries?
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22nd Feb 2014, 4:09 am | #16 |
Pentode
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Re: Why all those taps on 1920s H.T. batteries?
Thanks folks for the commentary.
Now that I think about it, here in the US we really did not have a audio pentode for BATTERY use until the advent of the octal based tubes of about 1938 such as the 1F4. (For example my handsome 1935 Atwater Kent model 768Q uses push-pull Type 30 triodes.) The only RF tetrode for BATTERY operation (1928) was the Type 22 until replaced by the Type 34 in 1932. And very few radios used them. So maybe that is why we were not so 'tap happy' in the late 1920's. Robert in the Carolinas |
22nd Feb 2014, 10:04 am | #17 |
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Re: Why all those taps on 1920s H.T. batteries?
I think there's something in Broadgage's 'experimental' comment.
Wireless had, of course, much more of an amateur enthusiast following in those days, and such a battery would serve as a 'bench supply'. |
22nd Feb 2014, 6:20 pm | #18 |
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Re: Why all those taps on 1920s H.T. batteries?
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22nd Feb 2014, 8:40 pm | #19 | |
Dekatron
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Re: Why all those taps on 1920s H.T. batteries?
Quote:
Paul Last edited by Paul_RK; 22nd Feb 2014 at 8:45 pm. |
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23rd Feb 2014, 2:26 am | #20 |
Pentode
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Re: Why all those taps on 1920s H.T. batteries?
Paul,
Thanks for the link to The Pye 555 instructions... I've been collecting American sets of the 1920s & early 30s since before 1967 and don't recall seeing such statements about moving a tap as the battery runs down... I thumbed thru a dozen or so of my oldest Wireless Worlds (early 1927) Not many battery adverts. But I did spot one interesting tidbit shown in one of these attached images... Sort of an explanation of why less is more... - I count the other battery as having 27 taps only one tap short of the Hellesens I posted at the start of this thread... Robert Last edited by RadioHist; 23rd Feb 2014 at 2:30 am. Reason: more info |