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A&R Transformers


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Guest Muon N'

With the OPT's, listed in this brochure as High Fidelity PP output transformers.

 

http://www.philipstorr.id.au/radio/technical/Australian%20Transformers%201.pdf

 

 

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182363791_Valvechart.jpg.15f049aaacecfab8f5a827b43c4ac1ce.jpg

 

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See March 1957 RTV&H for detailed specs on that output transformer.  It may not be good enough for the Williamson design, but excellent for a well made Mullard 5-10 or similar.

Edited by trobbins
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 To add to trobins  information; the transformers are designed for the Mullard 5/10 design. That  amplifier used 6BQ5/ EL84 valves in a pentode push pull mode. The A & R  OT 2525 transformer could be used in the normal or low loading mode. If an amplifier were to be constructed  based on this  design, some thought should be given to modifying the first  valve stage to reduce the high gain to better suit modern source equipment.

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Hi All, Thanks for info thus far, so, the seller of these tx was building a Mullard 5 10 using el84, which is not listed as a usable tube under “h” in the above table, can I use el34 in set mode as mono blocks, on two separate chassis ?

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1 hour ago, Digital Man said:

can I use el34 in set mode as mono blocks, on two separate chassis ?

No. The datasheet says they're PP transformers so they won't have sufficient air gap to allow the current required for SET.

 

Why anyone would want a SET though confounds me.

Edited by A9X
mo'wordses
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Sure you can if you are starting from scratch. 

 

Have you looked up the datasheets for those valves - what differences can you identify and how will you manage those differences if you are aiming for the 5-10 design? 

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28 minutes ago, Digital Man said:

but can I use el34’s as mono blocks in pp ?

Sure using the 6k p-p winding.

 

Here's an excellent serving suggestion, from the late Allen Wright. I've actually built these and they're quite good, butter than almost any vintage schematic I've tried.

 

image.png.b5e8c88c9e76ab170ba4aa1fc9a59d2c.png

 

image.png.72c8849dc0faad787c4c0f9361bafc80.png

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4 hours ago, Digital Man said:

Hi All, Thanks for info thus far, so, the seller of these tx was building a Mullard 5 10 using el84, which is not listed as a usable tube under “h” in the above table, can I use el34 in set mode as mono blocks, on two separate chassis ?

The 'H' does not apply to the OT 2525.  It appears that the  appropriate valve type was left out of the brochure. The power transformer is in-adequate for push pull operation of EL34 valves and given that all the transformers are from the 1950s caution must be taken as the insulation may not be fully effective.

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Guest Muon N'
4 hours ago, VanArn said:

The 'H' does not apply to the OT 2525.  It appears that the  appropriate valve type was left out of the brochure. The power transformer is in-adequate for push pull operation of EL34 valves and given that all the transformers are from the 1950s caution must be taken as the insulation may not be fully effective.

Ah, so my interpretation of that PDF was wrong! sorry about that @Digital Man

 

Edit: still looks like it to me, and where they have a dash indicated - then it has been left out, that's the way I see it in there, but like I said, sorry if I got it wrong.

But I'm no expert so take my posts with a pinch of salt.

Edited by Muon N'
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I would suggest that you will not have any trouble staying with the EL84 valve style as an output valve. These are readily available and there are higher rated equivalents such as the Russian type 6P14P that allow a greater power  output to be achieved with modifications to the amplifier circuits to make use of silicon diodes in the high voltage supply and the application of fixed bias.

  The only other valve type that would  suit is the 6L6GC beam tetrode as the  heater supply current is a modest 0.9 amp which is only slightly higher than that of the EL84. The screen voltage supply needs to be adjusted to suit this valve.

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An EL34 draws  1.5 amp of heater current. It would be o.k to wire  the  valves to the individual 6.3 volt supplies.  The operating points for the valve to determine the anode  and screen currents has to be taken into consideration as your power transformer has a current rating of 125mA for the B+ supply. This is an old transformer and care has to be taken as the insulation of the windings cannot be assured and running the transformer at full capacity could result in failure. There is no point in running EL34s in an amplifier where the performance has to be restricted to meet the limitations of the power supply and the O/P transformer. This would be an unwarranted design exercise when the Mullard 5/10 amplifier circuit already   serves as a guide.

 

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6 hours ago, VanArn said:

 

  The only other valve type that would  suit is the 6L6GC beam tetrode as the  heater supply current is a modest 0.9 amp which is only slightly higher than that of the EL84. The screen voltage supply needs to be adjusted to suit this valve.

 

Yes.  The extra heater current of the EL34 often makes it harder to use.  As well as the 6L6, you could step down in power to a 6V6 for example.  All still octal valves like the EL34

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The O/P transformer Is for push pull  pentode operation of the EL84  with the option of low loading. It is not designed  as  an ultra linear transformer.

Edited by VanArn
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Hi, Yes, push/pull only, not possible for single ended, I am thinking of using a pure pentode circuit for this project, old school, as an aside, what are the quality vintage A&R transformers like ?

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16 minutes ago, Digital Man said:

Hi, Yes, push/pull only, not possible for single ended, I am thinking of using a pure pentode circuit for this project, old school, as an aside, what are the quality vintage A&R transformers like ?

Pretty good IMO, especially if you run the valves, as suggested in that chart, as triodes in Class A.   It says they are only 10 watts, so 6V6's in pentode class AB PP will put out too much power - probably about 15 watts

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