Digital Man Posted April 17, 2019 Share Posted April 17, 2019 Hi All, What power tubes could be used with these A&R transformers ? I can get two of them the same, I am thinking mono blocks, in set mode of course. Thanks. Link to comment Share on other sites More sharing options...
Guest Muon N' Posted April 17, 2019 Share Posted April 17, 2019 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 Link to comment Share on other sites More sharing options...
trobbins Posted April 17, 2019 Share Posted April 17, 2019 (edited) 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 April 17, 2019 by trobbins Link to comment Share on other sites More sharing options...
VanArn Posted April 17, 2019 Share Posted April 17, 2019 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. Link to comment Share on other sites More sharing options...
Digital Man Posted April 17, 2019 Author Share Posted April 17, 2019 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 ? Link to comment Share on other sites More sharing options...
A9X Posted April 17, 2019 Share Posted April 17, 2019 (edited) 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 April 17, 2019 by A9X mo'wordses Link to comment Share on other sites More sharing options...
Digital Man Posted April 17, 2019 Author Share Posted April 17, 2019 Hi, Yes, I got the message about them being only used for pp rather than set in a earlier response, but can I use el34’s as mono blocks in pp ? Link to comment Share on other sites More sharing options...
trobbins Posted April 17, 2019 Share Posted April 17, 2019 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? Link to comment Share on other sites More sharing options...
A9X Posted April 17, 2019 Share Posted April 17, 2019 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. Link to comment Share on other sites More sharing options...
VanArn Posted April 18, 2019 Share Posted April 18, 2019 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. Link to comment Share on other sites More sharing options...
Guest Muon N' Posted April 18, 2019 Share Posted April 18, 2019 (edited) 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 April 18, 2019 by Muon N' Link to comment Share on other sites More sharing options...
Digital Man Posted April 18, 2019 Author Share Posted April 18, 2019 Hi, Okay, so the brochure does not faithfully list all usable valve types for these two power transformers ? So, what other tubes can I use ? Thanks Link to comment Share on other sites More sharing options...
VanArn Posted April 18, 2019 Share Posted April 18, 2019 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. 1 Link to comment Share on other sites More sharing options...
Digital Man Posted April 19, 2019 Author Share Posted April 19, 2019 Hi, Okay, so the heater supply won’t drive el34’s then ? Link to comment Share on other sites More sharing options...
VanArn Posted April 19, 2019 Share Posted April 19, 2019 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. 1 Link to comment Share on other sites More sharing options...
Digital Man Posted April 19, 2019 Author Share Posted April 19, 2019 Hi, Okay, I really appreciate the advice, I will not run the transformer beyond it’s scope. Thanks Link to comment Share on other sites More sharing options...
aussievintage Posted April 19, 2019 Share Posted April 19, 2019 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 Link to comment Share on other sites More sharing options...
Digital Man Posted April 19, 2019 Author Share Posted April 19, 2019 Hi, Yes, I could go with 6v6, something to think about Link to comment Share on other sites More sharing options...
trobbins Posted April 19, 2019 Share Posted April 19, 2019 Perhaps check if the preferred UL ratio is the same for 6V6 as for EL34, and the forward gain may change, so the feedback level may need to be altered to suit. Link to comment Share on other sites More sharing options...
aussievintage Posted April 19, 2019 Share Posted April 19, 2019 1 hour ago, trobbins said: Perhaps check if the preferred UL ratio is the same for 6V6 as for EL34, or triode wire them and forget the UL. Depends on power required. Triode mode might be much nicer. Link to comment Share on other sites More sharing options...
VanArn Posted April 19, 2019 Share Posted April 19, 2019 (edited) 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 April 19, 2019 by VanArn Additions. Link to comment Share on other sites More sharing options...
Digital Man Posted April 19, 2019 Author Share Posted April 19, 2019 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 ? Link to comment Share on other sites More sharing options...
aussievintage Posted April 19, 2019 Share Posted April 19, 2019 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 Link to comment Share on other sites More sharing options...
Digital Man Posted April 19, 2019 Author Share Posted April 19, 2019 Yes, or I may go with either el84 or 6l6, I can build two integrated mono blocks, I would do a completely new build as opposed to building the Mullard 5 10 Link to comment Share on other sites More sharing options...
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