Bottlehead Forum
Bottlehead Kits => Legacy Kit Products => Stereomour => Topic started by: Bonzo on July 18, 2013, 09:33:49 PM
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Good morning to everyone,
I was wondering if someone has ever tried to use #46 tube in Stereomour, and if it's possible.
I have a beautiful pair of Sylvania tubes and I'm also wondering of buying a Stereomour kit!
Thank you for your help!
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I don't know if I am reading Duncan's tube data right but it looks to be a single tetrode. The 12AT7 is a dual triode and both triodes are used. So if I have this right you would need the juice for two 46 tubes (heaters) and a new hole.
But don't let that be a stopper. Even if I am right you should try this to see what you think. My Paramours have 76 drivers in place of the 1AT7s that were there to start with.
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Thank you Grainger,
but I was thinking to use the 46 in place of the 2A3.
I red somewhere that the 46 can be use triode-strapped as a very good substitute of the 45.
Moreover a pair of NOS 46 costs a fraction of a pair of NOS 45, and they are reported to sound as good as 45.
Ciao!
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I used a 46 with an adapter in my SR 45. It didn't sound too great.
If you search the forum it was expressed that the 46 operating points were not ideally met by the sr45 as far as i can remember...
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It could be made to work, but the match between the Stereomour output iron and the 46 is probably less than ideal. IIRC the tube at standard RCA operating point of Vp=250, Va=22ma, Vg=-33 would like to see a 7K load. Not sure what the Stereomour's resistance is. Also consider that you are only going to get slightly more than one watt from this tube. Hope this is helpful.
Robert Lees
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Thank you very much for your information.
I feared a 46 couldn't be a direct raplacement in this amp... :(
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With an 8 Ohm speaker on the 4 Ohm tap on the Steremour, you'd reflect an 8K load to the 46, though hitting that operating in the Steremour may be a little tricky.
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The 46 is only specified at its intended application, but like all tubes it does not "know" what the application is ... :^)
As a Class-A triode, it was operated (with G2 connected to the plate) at 22mA to act as a triode driver, transformer-coupled to a pair (with G1 connected to G2) in Class B push-pull. But the plate it rated to dissipate 10 watts, the same as a 45, and the Cunningham spec sheet shows the Class A plate+G2 curves up to 80mA. There is no obvious reason not to use it as if it were a 45, at ca. 35mA current. The mu is a little higher, and the plate resistance a hair lower, but using cathode bias as in the Stereomour I'd expect fairly similar operating conditions.
That said, I have not tried it - so don't blame me if you fry the tube or something else goes wrong!
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Thank you very much Paul,
it would be nice to hear if someone tried a 46 in your design; in my opinion it should work, but I don't know very much about amp design, so they could work, but awfully ;D
Thank you again! Ciao!
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Your use of the term "intended application" has clarified a lot for me, thanks! I assume that class A operation is still limited to 250 volts?
Regards
Robert Lees
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Your use of the term "intended application" has clarified a lot for me, thanks! I assume that class A operation is still limited to 250 volts?
Regards
Robert Lees
Duncan Amps website tdls.duncanamps.com lists the max voltage for se operation of the 46 at 300vdc.
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300 volts is class b operation, have a look at the RCA data sheet.
Robert Lees
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The Cunningham data sheet shows 250v max for Class A (G2 wired to the plate) and 400v max plate voltage for Class B (G2 wired to G1).
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I started wondering about using a 46 after reading "the Bugle" scheme on Sound Practices and the one drawn by Gary Kaufman.
They both seems quite good from the entusiastic review of the builders.
Gary Kaufman's B+ was about 285v, if it could be useful...
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I started wondering about using a 46 after reading "the Bugle" scheme on Sound Practices and the one drawn by Gary Kaufman.
They both seems quite good from the entusiastic review of the builders.
Gary Kaufman's B+ was about 285v, if it could be useful...
I think you will be fine adopting this amp for a 46 tube. I looked at the expected voltage data for the 45 version of the stereomour. 350vdc before the plate choke, 340vdc on the plate. To determine plate voltage it is neccesary to subtract the cathode voltage drop. The cathode voltage drop is 57vdc. 340vdc - 57vdc is 283vdc, 283vdc is the expected plate voltage for this circuit with a 45. It would probably be about the same with a 46. These calculations were made based on line voltages of 119vac, if your line voltage is closer to 125vac, your plate voltage may be 10-20 volts higher then expected. If this is the case increase your bias supply resister from 1.2k to 1.5k or 1.8k. If your plate voltage is significantly more then expected and your line voltage is around 119vac and your cathode voltage drop is less then expected then you need to increase your cathode current by reducing your cathode resister from the stock 1.6k.