45 SE

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andrew Ivimey
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#136 Re: 45 SE

Post by andrew Ivimey »

Precisely.
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Paul Barker
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#137 Re: 45 SE

Post by Paul Barker »

Most would be dead if they did what I have done.
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andrew Ivimey
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#138 Re: 45 SE

Post by andrew Ivimey »

Well anyway, my point was that an input/ driver valve that is closer to a 45 vintage might be a good way to go.
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#139 Re: 45 SE

Post by Paul Barker »

Yes but he needs more than one voltage stage and all the us valves of that era are low mu. British are unobtaineum these days.
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andrew Ivimey
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#140 Re: 45 SE

Post by andrew Ivimey »

So I appreciate one weedy 76 even choke loaded is a tall order but why not try a 6sn7?

Back in the day when 45s were output valves in tabletop radios there must have been drivers other than say 6sj7.
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Nick
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#141 Re: 45 SE

Post by Nick »

Well anyway, my point was that an input/ driver valve that is closer to a 45 vintage might be a good way to go.
I have to ask why? Should he use 1930's wire and 1930's electricity?
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andrew Ivimey
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#142 Re: 45 SE

Post by andrew Ivimey »

Why are you being so aggressive Paul? Steve is able to decide for himself but his work evolves. If we can't suggest ideas without getting worked over then what's the point.

We all know your knowledge of electronics is encyclopedic but cannot I not contribute to the thread?
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#143 Re: 45 SE

Post by steve s »

Must say I agree with Paul and yourself , a driver that matched the era of the 45 valves would be my choice too but as Paul said they are getting rare.
I didn't read Paul's comments as being aggressive though Andrew. The opposite.. 😀🙂
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andrew Ivimey
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#144 Re: 45 SE

Post by andrew Ivimey »

To whom?
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#145 Re: 45 SE

Post by Nick »

Maybe its my post that is seen as aggressive> I just wondered why a 76 was better than a 6sn7 was better than a 5687 (other than the matching age), or just the ecc81 that was being used. I also like choke loaded 76's but it would need another stage as Paul said. One of my favourite "modern" highish mu valve is the 6072a, but as said a 6sn7 would also do the job.

But if I read what Steve posted, I think he was trying to add a bit of a curve to the response anyway instead of going for high linearity.
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#146 Re: 45 SE

Post by Paul Barker »

andrew Ivimey wrote: Thu Jun 17, 2021 9:05 pm To whom?
Sorry no emotion intended meant factually. Steve might want to keep his topology I’m not guiding him at all in this process.
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#147 Re: 45 SE

Post by Paul Barker »

Back on topic I’d try and get an ecc33 or better a British mu 40 iht from late ‘20’s. MH4 cv1678 Vary rare and more cost.
Last edited by Paul Barker on Thu Jun 17, 2021 11:22 pm, edited 1 time in total.
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#148 Re: 45 SE

Post by Cressy Snr »

I didn’t think my choice of driver would arouse such passions.
The fact that Paul and Mr I (yes, he is the mysterious benefactor) have let me have these 45s, is why I’ve got the best sound I’ve ever had at home and I can’t thank either of them enough for their generosity.

I’ve been working a bit more on the amp today and have added a little bit of additional hardware to the heater wiring in the form of a switch that allows me to choose between the ECC81 type and the ECC88/6922/6N1P types.

The diagram below, I found in my power supply book by Merlin Blencowe:
AED2E4B8-98E0-441C-BDF4-6EA600B194F6.jpeg
AED2E4B8-98E0-441C-BDF4-6EA600B194F6.jpeg (10.85 KiB) Viewed 2769 times
The switch can be seen behind the centre valve and it lets me choose which valve base type is in operation at any one time.
6781A566-058D-4643-9346-2E050118BD75.jpeg
6781A566-058D-4643-9346-2E050118BD75.jpeg (95.5 KiB) Viewed 2769 times
Position A gives ECC81 base heater wiring. Position B gives ECC88 base heater wiring.

I also changed the plate resistors from 15K to 27K. The LED bias allows each type to find its designed operating point without having to change cathode resistors, which is a useful facility to have.
I haven’t done any comparisons yet, but it all works, so I’ll have a go with some different valves tomorrow.
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#149 Re: 45 SE

Post by ACPEN »

Might I suggest as contemporary (ish) the 4D1 Brimar (12v htr) or Osram H30 (mu 40) or the Osram H42 (mu 100 - 4v htr) interesting specs for this one - all B7 base. H42 listed as suitable to drive PX4.
Used them all to good effect ....
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#150 Re: 45 SE

Post by ACPEN »

Re last post - Age related memory error(!)
H30 is mu 80 and has the interesting and unusual specs for the time.
😁
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