I've just found some 6aq5 tubes lying around, and looking at the gain of these things they have just about the right gain in triode mode for a (much needed) line stage. They should also have more than enough grunt 
Problem is, i have no experience designing tube circuits, and this is far from the normal application for these things. I've searched everywhere but can't find a thing.
If anyone could help me out with component values, i'd be most appreciative
Thanks,
Hamish
Problem is, i have no experience designing tube circuits, and this is far from the normal application for these things. I've searched everywhere but can't find a thing.
If anyone could help me out with component values, i'd be most appreciative
Thanks,
Hamish
What do you have available for a PS, and at what voltage? That'll be your starting point to determine what you can easily use for the B+, unless you're willing to get something made (muchos pesos in Oz) or use surplus.
It's unlikely many people have used this tube in this application, but I can't see why it won't sound good. Trouble is, you're going to have to find the op point yourself (which is why I asked about the PS).
An OTTOMH suggestion to start would be B+ = 400V, Ik = 30mA, Va = 150V, Rl = 8k (20W), or 300V B+ / 5k.
It's unlikely many people have used this tube in this application, but I can't see why it won't sound good. Trouble is, you're going to have to find the op point yourself (which is why I asked about the PS).
An OTTOMH suggestion to start would be B+ = 400V, Ik = 30mA, Va = 150V, Rl = 8k (20W), or 300V B+ / 5k.
Thanks for the reply, Brett. I've been meaning to build your 12B4A line stage but got side tracked with silicon 😱
It's good to get a little validation on the design. Seeing noone had used it before had me worried, but you've gotta try everything at least once (except folk dancing).
As for power, i've got a 250-0-250 little transformer (rather poor quality) that was in the AWA receiver that i got the tubes from. I also have a 350-0-350 R-core moster i bought a while back for the 12B4A that never was.......yet.
I figure if i can get this working with some junk stuff, then i can splash out a bit more on some real hardware.
Thanks again,
Hamish
It's good to get a little validation on the design. Seeing noone had used it before had me worried, but you've gotta try everything at least once (except folk dancing).
As for power, i've got a 250-0-250 little transformer (rather poor quality) that was in the AWA receiver that i got the tubes from. I also have a 350-0-350 R-core moster i bought a while back for the 12B4A that never was.......yet.
I figure if i can get this working with some junk stuff, then i can splash out a bit more on some real hardware.
Thanks again,
Hamish
It's not a bad little design. If you get around to it, I hope you like it.Hamish said:
I don't know that it'll sound, good, but I suspect it will. The 6AQ5's I've tried recently in another project were very good, and as a lot of people don't use them, cheap too.
I threw some estimate numbers into PSUD for both transformers and for simple SS FW rectification, got 420 and 320V for both channels off a single supply @ 30mA/tube.
Measure the transformer secondaries and futz with the numbers to see what you get. Even with the big one, and a couple of RC stages the 300V op point I mentioned is viable, if you don't mind a few extra watts of heat.
Everything I've suggested is available cheaply through local suppliers. If you like it this way, then I'd suggest using a FW with a 5AS4 or similar, LC (+LC if affordable; Hammonds are cheap) off the 700Vct transformer. Then by changing a couple of resistors and sockets, you can try the 12B4A too.
Thanks for your replies. I've modelled a few in PSUDesigner, and for now trying to get an CRCRC filter to work with R values of a sensible wattage. I want to try and use the cheap transformer, as i have the big one still planned for the 12B4A. I see Evatco have some reasonable open style chokes for around $30 a piece.
I'm just working my way through a tube design book now, so hopefully i'll be not so much in the dark. I found the sticky thread for newbies, so i'm devouring everything in there for now.
I do have to admit the 6AQ5's 8% THD is a little disturbing.....but this is a first project 🙂
Thanks again for your help and guidance, Brett 😉
Cheers.
I'm just working my way through a tube design book now, so hopefully i'll be not so much in the dark. I found the sticky thread for newbies, so i'm devouring everything in there for now.
I do have to admit the 6AQ5's 8% THD is a little disturbing.....but this is a first project 🙂
Thanks again for your help and guidance, Brett 😉
Cheers.
If you're going to use a SS rectifier, simply add a 100u cap at the first position. That got me the 320V I mentioned earlier. I like to use the constant current option for the load (even though I know it's not CC); in this example 60mA. Look at the voltage at the CCS, which is 20V high for the 300V op point. The R should be 20/60mA = 330R. I'd probably split the supplies after the first cap and run a seperate RC for each tube; say 650R and 220u. Not the best supply in the world, but it'll work and give you an idea whether it's worth refining the design.Hamish said:
The open frame Hammonds are quite good, and the 193's good for poweramps.
As I mentioned in the last post, you can build this using the bigger trans, and with a 4 resistor modification and some new sockets, use the 12B4A's later in the same setup. Just don't build it all fancy until you finalise it
You won't get but a tiny fraction of that trioded, working into a modest load and swinging the huge 1-2V a linestage will give.
My pleasure.
The 6AQ5 is similar to the 6BQ5/EL84 which i have seen mentioned for use in triode mode in a line stage.
dave
dave
Actually, the 6AQ5 is a 6V6 in a seven-pin miniature envelope, so trode-connected it should sound fine. Any triode that makes a good driver for a DHTSE output will usually make a good line out with suitable transformer when using longggg cales.
John
I actually wanted to try and avoid using an output transformer, and just go with a cap. I've found a couple of schematics using similar tubes in triode mode for headphone output (also some for the 6BQ5 (thanks for the tip, Dave), which i seem to remember are lurking inside my Akai R2R 
)
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Yep. And even better in {real} amps, ie PP's too.jlsem said:
The 6BQ5 is an excellent tube, but it generally has too much gain for a linestage, unless you Tx couple the output, which I think is a good idea anyway. Use Lundahls.Hamish said:I actually wanted to try and avoid using an output transformer, and just go with a cap. I've found a couple of schematics using similar tubes in triode mode for headphone output (also some for the 6BQ5 (thanks for the tip, Dave), which i seem to remember are lurking inside my Akai R2R
Do you use Circuit Maker Student to model your designs?
Here, I made this model last night of a triode-connected 6AQ5A - go nuts! 🙂
Use Notepad and just paste it in at the end of your "triode.sub" file in the "models" folder.
Here, I made this model last night of a triode-connected 6AQ5A - go nuts! 🙂
Code:
*Vacuum Tube Triode (Audio freq.) pkg:VT-7 (A:1,2,3)(B:6,7,8)
.SUBCKT X6AQ5A 1 3 4
B1 2 4 I=((URAMP((V(2,4)/8)+V(3,4)))^2.25)/15000
C1 3 4 8.5E-12
C2 3 1 8E-12
C3 1 4 0.4E-12
R1 3 5 10E+3
D1 1 2 DX
D2 4 2 DX2
D3 5 4 DX
.MODEL DX D(IS=1.0E-12 RS=1.0)
.MODEL DX2 D(IS=1.0E-9 RS=1.0)
.ENDS X6AQ5AUse Notepad and just paste it in at the end of your "triode.sub" file in the "models" folder.
Brett, does "your" 12B4A linestage invert phase if used with a standard capacitor output?
If yes, can this be fixed by reversing the output wires from the transformer when used in a parafeed construction?
If yes, can this be fixed by reversing the output wires from the transformer when used in a parafeed construction?
Hmmmm, not bad Geek. I might give it a try, but as i only have two tubes, one half of my stereo might get lonely 🙁
In relation to the above post, does running it as a triode with a cap output reverse phase?
Thanks for all the help, guys. i'll let you know when i get it all slapped together.
In relation to the above post, does running it as a triode with a cap output reverse phase?
Thanks for all the help, guys. i'll let you know when i get it all slapped together.
Yes, as do all common cathode stagesbequerel said:
Yes. But why not simpy reverse the speaker cables if you need to swap absolute phase rather than adding an output Tx?
Brett , if you are still with us on this thread:
I will have approx 125V (calculated) on the plates after the CCS in my 12B4A linestage.
(150V stabilized with 2xVR75 tubes - 25V loss in the CCS = 125V)
What would you suggest as an suitable bias point with the 125V plate voltage in mind?
Sorry for hijacking the thread!
I will have approx 125V (calculated) on the plates after the CCS in my 12B4A linestage.
(150V stabilized with 2xVR75 tubes - 25V loss in the CCS = 125V)
What would you suggest as an suitable bias point with the 125V plate voltage in mind?
Sorry for hijacking the thread!
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