Does anyone out there have a schematic for a type 27 pre amp
i've got the 27's and assorted bits n pieces. any help is most
welcome.
i've got the 27's and assorted bits n pieces. any help is most
welcome.
thank you Frank, i will have a bash at that over the weekend. I have seen a design for a 26 that has choke loading of the anode, what are the benefits of this ? . Would the 27 be better if choke loaded.
Hi,
The 26 and 27 are very similar so you could look at circuits using that too.
Burnedfingers had a thread running on that valve as well.
Choke loading offers a much higher impedance AC-wise than a resistively loaded design.
Final results will depend on implementation but in theory it should be better to use a choke.
Cheers,😉
The 26 and 27 are very similar so you could look at circuits using that too.
Burnedfingers had a thread running on that valve as well.
Choke loading offers a much higher impedance AC-wise than a resistively loaded design.
Final results will depend on implementation but in theory it should be better to use a choke.
Cheers,😉
Some people say the #27 holds the same promise the #26 does. I cannot comment on this as yet. I just received a 2.5V transformer today and will wire it in tomorrow for a try. The circuit will have two 150H chokes in series to the plate for each tube. I will try AC on the heaters first with the hopes that it might work. Looks like I will aim for 135Von the plate for the first go around.
Will post more tomorrow.
Joe
Will post more tomorrow.
Joe
Update
Wired in the heater transformer and fired it up today. It doesn't quite live up to the #26's performance. It is however very natural sounding without any microphonic problems. Its worth the time to play with. Running AC on the heaters with very little hum. Running 135volts on the plate and 9volts cathode voltage. Sounds very nice with 2) 150 H chokes in series to the plate.
Joe
Wired in the heater transformer and fired it up today. It doesn't quite live up to the #26's performance. It is however very natural sounding without any microphonic problems. Its worth the time to play with. Running AC on the heaters with very little hum. Running 135volts on the plate and 9volts cathode voltage. Sounds very nice with 2) 150 H chokes in series to the plate.
Joe
27 Line Amp
26 and 27 are very close regarding µ, Ia and Rp, but 27 is pretty easy to heat. Just AC heating and it works fine. For 26 you will need a regulated DC supply in most cases.
Running with 135v Ua and -9V Ug the Rp of 27 is 11kohms.
For 11kohms Ri a choke starts to work series with 150H, it delivers -1db at 45Hz and - 3dB at 12Hz.
Regards
Ralf
26 and 27 are very close regarding µ, Ia and Rp, but 27 is pretty easy to heat. Just AC heating and it works fine. For 26 you will need a regulated DC supply in most cases.
Running with 135v Ua and -9V Ug the Rp of 27 is 11kohms.
For 11kohms Ri a choke starts to work series with 150H, it delivers -1db at 45Hz and - 3dB at 12Hz.
Regards
Ralf
Drop the chokes or keep them?
RS
Is it your feeling the chokes should be dropped in favor of a plate resistor? That is the notion I get when I read your response that it is 3db down at 12HZ.
Anyone else have any feelings on this?
Joe
RS
Is it your feeling the chokes should be dropped in favor of a plate resistor? That is the notion I get when I read your response that it is 3db down at 12HZ.
Anyone else have any feelings on this?
Joe
Re: Drop the chokes or keep them?
I like plate chokes and interstage coupling pretty much. But with circa 10k Rp the critical value is reached. With very high inductive chokes you can underrun the cut-off at bass frequencies, but one should take care about parasitic capacities of the windings.
From my point of view -3dB at 12Hz is still fair; in most cases the complete system including speakers can not perfom on this level.
Regards
Ralf
burnedfingers said:
I like plate chokes and interstage coupling pretty much. But with circa 10k Rp the critical value is reached. With very high inductive chokes you can underrun the cut-off at bass frequencies, but one should take care about parasitic capacities of the windings.
From my point of view -3dB at 12Hz is still fair; in most cases the complete system including speakers can not perfom on this level.
Regards
Ralf
Re: Drop the chokes or keep them?
Keep the chokes. With two in series, you have 300H, not the 150H of RS's calc so your f3 should be around 6Hz not factoring in the 7k4 winding resistance of the two of them.
burnedfingers said:
burnedfingers said:
Keep the chokes. With two in series, you have 300H, not the 150H of RS's calc so your f3 should be around 6Hz not factoring in the 7k4 winding resistance of the two of them.
I knocked together the 27 pre last weekend. The sound is amazing i'll never go back to my accuphase pre, althouth the accuphase does have better facilities 🙂
I am using my power supply chokes in the anode feed, these are 450H. I want to go back to a valve rectifier using 5u4g, as i have a few. The problem is i no longer have the chokes, can i use a capacitor filter and if so is there a simple way to work out the required C and R.
thanks in advance, peter.
I am using my power supply chokes in the anode feed, these are 450H. I want to go back to a valve rectifier using 5u4g, as i have a few. The problem is i no longer have the chokes, can i use a capacitor filter and if so is there a simple way to work out the required C and R.
thanks in advance, peter.
Peter
I suggest you put the chokes back in the power supply and purchase several plate resistors and see if you can detect a difference. I have done this and I like the #27 with plate resistors as opposed to plate chokes. Just my .02
J
I suggest you put the chokes back in the power supply and purchase several plate resistors and see if you can detect a difference. I have done this and I like the #27 with plate resistors as opposed to plate chokes. Just my .02
J
Gday J,
Thanks for your advice, i had already given up on the chokes they are back in my supply. I'm currently using 130R on the anode, I hate to say this, the tube type decides which resistance should be used. I have some deforest 427 with the punched shiny anode and a nipple on top. these run with 130, the 427's with the mesh anode run 150. I have lots of other 27's to try and it is quite a task.
Thanks for your advice, i had already given up on the chokes they are back in my supply. I'm currently using 130R on the anode, I hate to say this, the tube type decides which resistance should be used. I have some deforest 427 with the punched shiny anode and a nipple on top. these run with 130, the 427's with the mesh anode run 150. I have lots of other 27's to try and it is quite a task.
Peter
I'm using 50K plate resistors and have 180volts on the plate and 12volts across the cathode resistor and it sounds every bit as good as the #26 did.
J
I'm using 50K plate resistors and have 180volts on the plate and 12volts across the cathode resistor and it sounds every bit as good as the #26 did.
J
Hi!
I am currently building a #27 pre for my brother. It will be loaded by Gary Pimms BBMCCCS, using the mu output.
Check out http://www.angelfire.com/ut/Likkhalt/index3.htm
to see schematic plus construction pic's so far.
I really look foreward to listen to this pre, I think it will be a stunner!! The tubes will be AC heated, so I hope I dont runn into problems with hum. I'll keep you posted about the sound when I get it running.
stigla
I am currently building a #27 pre for my brother. It will be loaded by Gary Pimms BBMCCCS, using the mu output.
Check out http://www.angelfire.com/ut/Likkhalt/index3.htm
to see schematic plus construction pic's so far.
I really look foreward to listen to this pre, I think it will be a stunner!! The tubes will be AC heated, so I hope I dont runn into problems with hum. I'll keep you posted about the sound when I get it running.
stigla
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