Hi
The idea is to do a 2-stage 845 SE, using a 45.
It has been done commercially by Electronluv (Ed Sawyer has one). There’s Ed says, is basically:
Input transformer (600: 15k???) >
45 (B+ about 200 v) >
1:1 5k IT >
45 output (900 v) >
(And parafeed output trans/ plate choke).
Ed has pointed out that the key to doing an 45-845 in two stages is (not just the driver tube alone) but getting enough gain, hence the use of a step-up input transformer. It would need to be a good quality step-up trannie (maybe custom) – eg James, Electraprint.
Making it a tad easier, 10 watts would do: the priority is hearing the sonics of the sweet 45, with 4-6 times the power, with a minimum of extra “layers”.
I believe long time 845er Grover Gardner DIYed one, but neither Ed nor Grover has a schematic . . hence my question
Recent 'underwhelm-ment' with some much touted SS amps has heightened my enthusiam.
So does anyone know the logic to calc the required specs of an input step up transformer, into a 45, to allow it drive the 845 to about 10 watts? 😕
Thanks
The idea is to do a 2-stage 845 SE, using a 45.
It has been done commercially by Electronluv (Ed Sawyer has one). There’s Ed says, is basically:
Input transformer (600: 15k???) >
45 (B+ about 200 v) >
1:1 5k IT >
45 output (900 v) >
(And parafeed output trans/ plate choke).
Ed has pointed out that the key to doing an 45-845 in two stages is (not just the driver tube alone) but getting enough gain, hence the use of a step-up input transformer. It would need to be a good quality step-up trannie (maybe custom) – eg James, Electraprint.
Making it a tad easier, 10 watts would do: the priority is hearing the sonics of the sweet 45, with 4-6 times the power, with a minimum of extra “layers”.
I believe long time 845er Grover Gardner DIYed one, but neither Ed nor Grover has a schematic . . hence my question
Recent 'underwhelm-ment' with some much touted SS amps has heightened my enthusiam.
So does anyone know the logic to calc the required specs of an input step up transformer, into a 45, to allow it drive the 845 to about 10 watts? 😕
Thanks
Re: required specs of an input step up transformer, into a 45, to allow it drive an 845
Inside joke (sort of): Crowhurst!
Inside joke (sort of): Crowhurst!
the details
I looked up the schematic for these amps last night. They use mainly custom Electraprint iron with silver windings, here's the basic details:
input trans: 1k to 15k (600 to 10k would also work or 600 to 15k)
45 runs at about 200v B+, battery biased. DC filaments.
1:1 IT (5k nominal rating, hopefully something like 40-50h+ would be nice, or parafeed it if you want with a 150h+ plate choke)
845 runs at about 900v B+, 5k:8 ohm Parafeed output trans, EI 125 lams. Battery and 1k cathode resistor bias. AC or DC fils (DC for lowest noise). 200h+ plate choke @ 100ma. approx 1-3uf parafeed bypass cap.
That's pretty much it. Power supplies depend on what you are into. These run MV rectifiers in a dual LCLCLC supply setup. You can tweak op points based on where you want the B+ to run. LMK if you get any further with this and I can provide any other details if needed.
Duplicating the amps exactly would be difficult, as sometimes Josh's work differed from the schematic, plus all the iron was custom anyway. But it's a good start (the above info)
thanks
-ED
I looked up the schematic for these amps last night. They use mainly custom Electraprint iron with silver windings, here's the basic details:
input trans: 1k to 15k (600 to 10k would also work or 600 to 15k)
45 runs at about 200v B+, battery biased. DC filaments.
1:1 IT (5k nominal rating, hopefully something like 40-50h+ would be nice, or parafeed it if you want with a 150h+ plate choke)
845 runs at about 900v B+, 5k:8 ohm Parafeed output trans, EI 125 lams. Battery and 1k cathode resistor bias. AC or DC fils (DC for lowest noise). 200h+ plate choke @ 100ma. approx 1-3uf parafeed bypass cap.
That's pretty much it. Power supplies depend on what you are into. These run MV rectifiers in a dual LCLCLC supply setup. You can tweak op points based on where you want the B+ to run. LMK if you get any further with this and I can provide any other details if needed.
Duplicating the amps exactly would be difficult, as sometimes Josh's work differed from the schematic, plus all the iron was custom anyway. But it's a good start (the above info)
thanks
-ED
Hi Ed
Thank you!
mainly custom Electraprint iron ~ ooh mucho $
Duplicating the amps exactly would be difficult
I see your point.
For those who don’t visit the Tube DIY Asylum, some alternatives *without input step up transformers emerge here:
www.audioasylum.com/forums/tubediy/messages/108682.html
www.audioasylum.com/forums/tubediy/messages/108614.html
Cheers
Thank you!
mainly custom Electraprint iron ~ ooh mucho $
Duplicating the amps exactly would be difficult
I see your point.
For those who don’t visit the Tube DIY Asylum, some alternatives *without input step up transformers emerge here:
www.audioasylum.com/forums/tubediy/messages/108682.html
www.audioasylum.com/forums/tubediy/messages/108614.html
Cheers
Heya. I'm the Jim who did the V3,V4 and V5 low-voltage 845 amp schematics
that people seem to link to alot.
A two stage high power 845 amp is possible, however, there are tradeoffs to
how and where you get the voltage gain required to drive the 845's grid to
full power. Lets look at tradeoffs.
Option 1:
You could use 45 driver with a 1:2 stepup transformer. However, the transformer will now reflect the Miller Capacitance + Transformer stray capacitance towards the preamp and cable. This will force some extreme requirements on your preamp: You will need a very low output impedance preamp that not only has tons of current grunt but also an output level of +10V. There are solid state preamps
that do this job very well. You will surely be building ANOTHER tube preamp, or
tube line buffer, with stepdown line out transformer 🙂 to get the drive and low impedance you need. On the other hand, a solid state differential line driver
(i.e. Analog SSM2142 or AD815), might sound better and be far cheaper. 🙂
Option 2:
You could use a single high gM tube driving a 1:2 interstage. Consider a
7788/E810F (gain=52, Rp around 700 ohms). Other tubes include the 6C45
or the EC8010/EC8020. You'd use the Lundahl LL1660/25mA in the 1:2 stepup
mode. This too will work, however, you are at the mercy of finding driver
tubes with matched gain. You will also be at the mercy of UHF oscillation and your circuit will need treatment to avoid the excitement of parasitic oscillations.
Option 3:
You could do what I did. Use a 1:1 interstage. Simulate "two stage" by using
a direct coupled driver of the interstage. Direct coupling eliminates a phase
shift which eliminate the problem with 3-stage amps - stability. If you chose
to go 3-stage, you can. 🙂 This seems to have the fewest tradeoffs. High Z input stage, easily produced voltage gain with simple devices, stability.
In the end, keep the input transformer (1:1) regardless of what option you choose. Moving balanced signals around your house is so much easier than
single ended (no ground loops, etc). In addition, I like the galvanic isolation
that exists between my amp chassis, and my low-voltage, finger friendly shelf of source devices.
-- Jim
that people seem to link to alot.
A two stage high power 845 amp is possible, however, there are tradeoffs to
how and where you get the voltage gain required to drive the 845's grid to
full power. Lets look at tradeoffs.
Option 1:
You could use 45 driver with a 1:2 stepup transformer. However, the transformer will now reflect the Miller Capacitance + Transformer stray capacitance towards the preamp and cable. This will force some extreme requirements on your preamp: You will need a very low output impedance preamp that not only has tons of current grunt but also an output level of +10V. There are solid state preamps
that do this job very well. You will surely be building ANOTHER tube preamp, or
tube line buffer, with stepdown line out transformer 🙂 to get the drive and low impedance you need. On the other hand, a solid state differential line driver
(i.e. Analog SSM2142 or AD815), might sound better and be far cheaper. 🙂
Option 2:
You could use a single high gM tube driving a 1:2 interstage. Consider a
7788/E810F (gain=52, Rp around 700 ohms). Other tubes include the 6C45
or the EC8010/EC8020. You'd use the Lundahl LL1660/25mA in the 1:2 stepup
mode. This too will work, however, you are at the mercy of finding driver
tubes with matched gain. You will also be at the mercy of UHF oscillation and your circuit will need treatment to avoid the excitement of parasitic oscillations.
Option 3:
You could do what I did. Use a 1:1 interstage. Simulate "two stage" by using
a direct coupled driver of the interstage. Direct coupling eliminates a phase
shift which eliminate the problem with 3-stage amps - stability. If you chose
to go 3-stage, you can. 🙂 This seems to have the fewest tradeoffs. High Z input stage, easily produced voltage gain with simple devices, stability.
In the end, keep the input transformer (1:1) regardless of what option you choose. Moving balanced signals around your house is so much easier than
single ended (no ground loops, etc). In addition, I like the galvanic isolation
that exists between my amp chassis, and my low-voltage, finger friendly shelf of source devices.
-- Jim
Hi Jim
Ah the man behind the circuits - thanks for your further information!
BTW, which of your three versions do you prefer?
Personally I don’t seek high power, *as long as dynamics aren’t compromised, 10 watts is *plenty.
Option 2:
Interesting, though 7788/ E810F/ 6C45/ EC8010/EC8020 don’t appeal greatly. I would prefer DHT or at least DHP (eg the 47) . .
Option 3 might be good if Option 1 can’t be made to work well with what I have ~
Option 1:
A SS preamp is not heresy, if you think it good enough to not introduce grain etc. Where for a * Good Analog SSM2142 or AD815 circuit (Analog’s site??)
as I have a potentially suitable preamp: the Mapletree Magic 5 -
For a 45 with a 1:2 step-up, a preamp is needed with:
· very low output impedance
· has tons of current grunt
· an output level of +10 V.
* Output Impedance
I will be using an autoformer (TVC). Their output impedance varies with volume, but in most listening will only be (I only just learnt this, hope I got it right)
e.g. 10% volume: 1 volt from the CDP; TVC out of 0.1 volt:
Output impedance = 100 R / ((1/0.1) squared)
= 100/ (10*10)
= 1 R
So at 10% volume, the output impedance is only 1 R.
At 50% volume (i.e. loud!), 1 volt, TVC out of 0.5 volt
Output impedance = 100R/ ((1/0.5) squared)
= 100 /4
= 25 R
As the most likely drivers are 98 dB, output impedances of 0.5 – 10R should be low enough?
* Output Level
The Magic 5 into a load of 20 K or more, outputs well over 10 V rms.
* Grunt
How many mA in a ton? 😉
Into a power amp, the Magic 5 current delivered depends on the input resistance of the power amp. At 100 K load and 4 V peak (around 3 V rms), current would be 0.04 mA peak (around 0.1 mW)
I have to check what would happen if bypassing the pre’s volume control with a TVC.
Does Option 1 with that pre leave anything not addressed
Thanks
Ah the man behind the circuits - thanks for your further information!
BTW, which of your three versions do you prefer?
Personally I don’t seek high power, *as long as dynamics aren’t compromised, 10 watts is *plenty.
Option 2:
Interesting, though 7788/ E810F/ 6C45/ EC8010/EC8020 don’t appeal greatly. I would prefer DHT or at least DHP (eg the 47) . .
Option 3 might be good if Option 1 can’t be made to work well with what I have ~
Option 1:
A SS preamp is not heresy, if you think it good enough to not introduce grain etc. Where for a * Good Analog SSM2142 or AD815 circuit (Analog’s site??)
as I have a potentially suitable preamp: the Mapletree Magic 5 -
For a 45 with a 1:2 step-up, a preamp is needed with:
· very low output impedance
· has tons of current grunt
· an output level of +10 V.
* Output Impedance
I will be using an autoformer (TVC). Their output impedance varies with volume, but in most listening will only be (I only just learnt this, hope I got it right)
e.g. 10% volume: 1 volt from the CDP; TVC out of 0.1 volt:
Output impedance = 100 R / ((1/0.1) squared)
= 100/ (10*10)
= 1 R
So at 10% volume, the output impedance is only 1 R.
At 50% volume (i.e. loud!), 1 volt, TVC out of 0.5 volt
Output impedance = 100R/ ((1/0.5) squared)
= 100 /4
= 25 R
As the most likely drivers are 98 dB, output impedances of 0.5 – 10R should be low enough?
* Output Level
The Magic 5 into a load of 20 K or more, outputs well over 10 V rms.
* Grunt
How many mA in a ton? 😉
Into a power amp, the Magic 5 current delivered depends on the input resistance of the power amp. At 100 K load and 4 V peak (around 3 V rms), current would be 0.04 mA peak (around 0.1 mW)
I have to check what would happen if bypassing the pre’s volume control with a TVC.
Does Option 1 with that pre leave anything not addressed
Thanks
I would go with the 45. The output tubes will never sound better than the drivers.
I think 20k (as in 600:20k) will work as well. The 20k the gurus here will need to confirm.
I would use interstage transformers as well.
Chance is that guys like Ken Shindo have been wrong about everything for 30 yrs. You can believe that if you want.
There are only one of two reasons Shindo gear sounds the way it does. Magic tubes. Or input, interstage and, in case of preamps, output transformers.
I think 20k (as in 600:20k) will work as well. The 20k the gurus here will need to confirm.
I would use interstage transformers as well.
Chance is that guys like Ken Shindo have been wrong about everything for 30 yrs. You can believe that if you want.
There are only one of two reasons Shindo gear sounds the way it does. Magic tubes. Or input, interstage and, in case of preamps, output transformers.
> I would go with the 45. The output tubes will never sound better than the drivers.
I'm a babe in the world of tubes, but tend to agree
Chance is that guys like Ken Shindo have been wrong about everything for 30 yrs. You can believe that if you want.
I haven't heard of Ken Shindo:
> only one of two reasons Shindo gear sounds the way it does
which I take it is really good in some or several ways . . ?
What is his site?
Cheers
I'm a babe in the world of tubes, but tend to agree
Chance is that guys like Ken Shindo have been wrong about everything for 30 yrs. You can believe that if you want.
I haven't heard of Ken Shindo:
> only one of two reasons Shindo gear sounds the way it does
which I take it is really good in some or several ways . . ?
What is his site?
Cheers
http://www.shindo-laboratory.co.jp
http://www.shindolabs.com
DH guru Susumu Sakuma has some interesting amps here ("The list of Sakuma's works"): http://www10.big.or.jp/~dh
http://www.shindolabs.com
DH guru Susumu Sakuma has some interesting amps here ("The list of Sakuma's works"): http://www10.big.or.jp/~dh
If 10W are your requirement, I'd shoot for an 845 running fixed
bias with anywhere from 550 - 600VDC on the plate with about 80mA at idle. That gets you 9'ish to 10ish watts. The search for a plate transformer will be harder than the output transformer. A possibility would be to obtain a 120/240 to 480VAC industrial control transformer and run it in reverse. The 480VAC, rectified and CLC filtered will get you a healthy 600V+.
Anything about 430V, I'd use the IT version rather than the LC coupled version. The reason being is that the LC coupling cap spans alot of potential (550V at idle!) and should or when it fail, it can take down your output transformer as well as fixed bias supply. The IT is simply a more reliable part. At 430V or so, however, I find the LC coupled version to sound every bit as good as the IT coupled version.
Re-jigger the driver stage... Go for a #45 with a #76 or #56 driver. Golden.
-- Jim
bias with anywhere from 550 - 600VDC on the plate with about 80mA at idle. That gets you 9'ish to 10ish watts. The search for a plate transformer will be harder than the output transformer. A possibility would be to obtain a 120/240 to 480VAC industrial control transformer and run it in reverse. The 480VAC, rectified and CLC filtered will get you a healthy 600V+.
Anything about 430V, I'd use the IT version rather than the LC coupled version. The reason being is that the LC coupling cap spans alot of potential (550V at idle!) and should or when it fail, it can take down your output transformer as well as fixed bias supply. The IT is simply a more reliable part. At 430V or so, however, I find the LC coupled version to sound every bit as good as the IT coupled version.
Re-jigger the driver stage... Go for a #45 with a #76 or #56 driver. Golden.
-- Jim
Cutting the excess, but where
Hi Jim
It occurred to me overnight that as the Input stage, I could use the Gordon Rankin Bugle 45 SE ~ (I bought all good components) ~ and am about to commence building.
Note “grunt’ can be interpreted in different ways:
eg max power, or dynamics within that max power, etc
With reasonable drivers & SPLs, the former doesn’t really concern me; but I *really want to *maximise micro & macro dynamics.
Would 600 V & about 80 mA compromise dynamics? .
. . with a combination of the Bugle & good ITs, hence the V & mA that can be fed to the power amp . .
Looming fly in the ointment – gain stages.
While not an absolute bogey man, as it stands, gain stages are:
Pre (Aksa/ Magic 5) 2 ( I have the Aksa & the Magic kit)
The Bugle 2
Typical power amp 3
Total “Scenario 1” 7 my comment: WTF?
And that’s before adding in the iron ‘stages’ . .
To streamline, yet get step-up to give 10 w with good dynamics?
How’s this (probably big errors here):
Preamp (low output impedance, ? current, output +10V)
\/
TVC
\/
1:5 step up auto-former I was offered free. Useful here#??
+
1:2 step up? (To give total 1: 10?)
\/
Bugle 45 (two stage, 6072 > 45)
\/
1:1 interstage (I would have used the 1: 10 here, but 1:1 is recommended )
\/
845
The $64 k question:
In this situation, would the best 845 circuit be the final stage of one of your 845 circuits?
Instead of using a power amp with three stages, that would result in a reduced total of five stages.
Tho still seems excessive - wrong somewhere: where to cut more/ replace with good ITs?
Thanks & Cheers
Hi Jim
It occurred to me overnight that as the Input stage, I could use the Gordon Rankin Bugle 45 SE ~ (I bought all good components) ~ and am about to commence building.
Note “grunt’ can be interpreted in different ways:
eg max power, or dynamics within that max power, etc
With reasonable drivers & SPLs, the former doesn’t really concern me; but I *really want to *maximise micro & macro dynamics.
Would 600 V & about 80 mA compromise dynamics? .
. . with a combination of the Bugle & good ITs, hence the V & mA that can be fed to the power amp . .
Looming fly in the ointment – gain stages.
While not an absolute bogey man, as it stands, gain stages are:
Pre (Aksa/ Magic 5) 2 ( I have the Aksa & the Magic kit)
The Bugle 2
Typical power amp 3
Total “Scenario 1” 7 my comment: WTF?
And that’s before adding in the iron ‘stages’ . .
To streamline, yet get step-up to give 10 w with good dynamics?
How’s this (probably big errors here):
Preamp (low output impedance, ? current, output +10V)
\/
TVC
\/
1:5 step up auto-former I was offered free. Useful here#??
+
1:2 step up? (To give total 1: 10?)
\/
Bugle 45 (two stage, 6072 > 45)
\/
1:1 interstage (I would have used the 1: 10 here, but 1:1 is recommended )
\/
845
The $64 k question:
In this situation, would the best 845 circuit be the final stage of one of your 845 circuits?
Instead of using a power amp with three stages, that would result in a reduced total of five stages.
Tho still seems excessive - wrong somewhere: where to cut more/ replace with good ITs?
Thanks & Cheers
Oh, thats an easy question! V5. The one with 1:1 IT coupling
and the "flexible" driver stage tube options.. V5 is actually capable of being a 2-stage system (no preamp!) at 750V/90mA with a total of 15W SE power. How?
I think 750V/90mA is the max practical power point. Above that,
and transformers and oil caps suddenly become big, expensive an
hard to find. What's required at 750V?
First, you need -100V of grid bias. That's real easy. A 0B2 gas
reference tube gives a clean 105V that you can feed to the secondary of the interstage.
With -100V at the grid, you need 200V of swing to the 845 to take it full power. Assuming a 2V input from a CD player, that means you need a gain of 100. Well, with direct coupling, thats
very easy because mu's multiply. So, a 76/6P5 with gain=13 and
a KT66/KT88 with a gain of 9 will definitely do the job.... Or, you
can use a 6C5/6J5 with gain=20 and a 6W6 with gain=6. Other
options include the 6J5 with a 45 (gain=5). The resistors in the
direct coupling stage pretty much stay the same regardless of what tube you put in those sockets. 🙂 So long as you stick to the 76/6SN7 family in the first tube and any octal triode-wired pentode in the second socket. In any case, you simply put a
100K passive attenuator at the input (assuming 2V signal from an upstread CD source) and you are completely DONE. 🙂
I know you are interested in "other tubes", but you really should try the myriad tube options I mentioned using 6V6/6W6/KTxx/EL43 type drivers! The main reason is the circuit is stable with the common and easy to find resistor values I've given. If you move to a different tube, you will have to recompute all the direct coupling values and possibly have more complexity formulating the resistor values needed.
V5 is a really cool amp topology because you can do so many things with it - even with myriad operating points. It's ideally suited though, for economy and flexibility, for 750V/90mA. At
that point, you are running the 845 at 75W plate dissipation (!!!)
This is the deep Class A operating people that you wont see the chinese amps doing (they run at 60W dissipation).
-- Jim
and the "flexible" driver stage tube options.. V5 is actually capable of being a 2-stage system (no preamp!) at 750V/90mA with a total of 15W SE power. How?
I think 750V/90mA is the max practical power point. Above that,
and transformers and oil caps suddenly become big, expensive an
hard to find. What's required at 750V?
First, you need -100V of grid bias. That's real easy. A 0B2 gas
reference tube gives a clean 105V that you can feed to the secondary of the interstage.
With -100V at the grid, you need 200V of swing to the 845 to take it full power. Assuming a 2V input from a CD player, that means you need a gain of 100. Well, with direct coupling, thats
very easy because mu's multiply. So, a 76/6P5 with gain=13 and
a KT66/KT88 with a gain of 9 will definitely do the job.... Or, you
can use a 6C5/6J5 with gain=20 and a 6W6 with gain=6. Other
options include the 6J5 with a 45 (gain=5). The resistors in the
direct coupling stage pretty much stay the same regardless of what tube you put in those sockets. 🙂 So long as you stick to the 76/6SN7 family in the first tube and any octal triode-wired pentode in the second socket. In any case, you simply put a
100K passive attenuator at the input (assuming 2V signal from an upstread CD source) and you are completely DONE. 🙂
I know you are interested in "other tubes", but you really should try the myriad tube options I mentioned using 6V6/6W6/KTxx/EL43 type drivers! The main reason is the circuit is stable with the common and easy to find resistor values I've given. If you move to a different tube, you will have to recompute all the direct coupling values and possibly have more complexity formulating the resistor values needed.
V5 is a really cool amp topology because you can do so many things with it - even with myriad operating points. It's ideally suited though, for economy and flexibility, for 750V/90mA. At
that point, you are running the 845 at 75W plate dissipation (!!!)
This is the deep Class A operating people that you wont see the chinese amps doing (they run at 60W dissipation).
-- Jim
Hi
Yes 1:1 IT coupling makes best sense for this.
And flexible drivers is the way to go. So . .
(My aim being driver stages swappable for the separate Bugle amp) . .
A tube experienced friend firmly believes that the IT must be sited in the Bugle amp as ‘driver’, because of the voltages leading into it.
However to allow different driver stages off-board amps, it makes sense to me to put the IT in the 845 amp stage, and run an umbilical in. Can that be made safe?
Maybe it could help a little if the two amps abutted? Like a mother-baby 😉
The 845 possibly being a two stage appeals a lot too. I believe it’s also possible with 12GN7’s, and high transconductance German tubes eg C3m.
How can I determine what IT specs would allow the 845 to be driven by any or at least most of, in approx order the 45/ 6w6/ 47/ C3m/ 12GN7/ EL34.
(If some need a one stage pre, that’s ok).
what is deep Class A?
I also like lower volts ~
The view that you get better sound as you push the 845: with max dissipation is 100, so 750 at 130 mA gives 98, or 120 mA is still only 90. Would those op points require just value changes in V5, or something more?
(Note I already have some good OPTs, which are 10 k)
Cheers
richard
Yes 1:1 IT coupling makes best sense for this.
And flexible drivers is the way to go. So . .
(My aim being driver stages swappable for the separate Bugle amp) . .
A tube experienced friend firmly believes that the IT must be sited in the Bugle amp as ‘driver’, because of the voltages leading into it.
However to allow different driver stages off-board amps, it makes sense to me to put the IT in the 845 amp stage, and run an umbilical in. Can that be made safe?
Maybe it could help a little if the two amps abutted? Like a mother-baby 😉
The 845 possibly being a two stage appeals a lot too. I believe it’s also possible with 12GN7’s, and high transconductance German tubes eg C3m.
How can I determine what IT specs would allow the 845 to be driven by any or at least most of, in approx order the 45/ 6w6/ 47/ C3m/ 12GN7/ EL34.
(If some need a one stage pre, that’s ok).
what is deep Class A?
I also like lower volts ~
The view that you get better sound as you push the 845: with max dissipation is 100, so 750 at 130 mA gives 98, or 120 mA is still only 90. Would those op points require just value changes in V5, or something more?
(Note I already have some good OPTs, which are 10 k)
Cheers
richard
I'd keep the IT wherever it's driver tube lives. Run the high level
signal from the IT secondary into the 845's chassis using coax... Tie the shield of the coax to the negative DC bias level, rather than ground. Very important to do that.
With fixed bias, its utterly critical to insure the wiring is reliable so you never lose the fixed DC bias voltage from the 845. 845 with a floating grid turns into a 1K power resistor.
You IT needs an Lpri of 30-40H to take tubes like a 45 with full response down past 20Hz. You need to be able to throw upwards of 300Vrms through it for a 1200V 845 and downwards of 60Vrms for an 845 running around 450V. The ElectraPrint 3033 is excellent! And the price is right. The E-P also takes a bias current of 40mA which means you can use little tubes (i.e. 6C45, 12GN7) or big tubes like the 45 and EL34. The Lundahls are very good to, but have a much smaller operating current sweetspot. You'd need an LL1660/35 for an EL34 or 45 and perhaps a 1660/18 for a 6C45
Lundahl is the only IT I know that will do 1:2 stepup IT. I'd not
advise doing it, unless you are committed to small high-gm UHF tubes as drivers.
-- Jim
signal from the IT secondary into the 845's chassis using coax... Tie the shield of the coax to the negative DC bias level, rather than ground. Very important to do that.
With fixed bias, its utterly critical to insure the wiring is reliable so you never lose the fixed DC bias voltage from the 845. 845 with a floating grid turns into a 1K power resistor.
You IT needs an Lpri of 30-40H to take tubes like a 45 with full response down past 20Hz. You need to be able to throw upwards of 300Vrms through it for a 1200V 845 and downwards of 60Vrms for an 845 running around 450V. The ElectraPrint 3033 is excellent! And the price is right. The E-P also takes a bias current of 40mA which means you can use little tubes (i.e. 6C45, 12GN7) or big tubes like the 45 and EL34. The Lundahls are very good to, but have a much smaller operating current sweetspot. You'd need an LL1660/35 for an EL34 or 45 and perhaps a 1660/18 for a 6C45
Lundahl is the only IT I know that will do 1:2 stepup IT. I'd not
advise doing it, unless you are committed to small high-gm UHF tubes as drivers.
-- Jim
Jim
Not being exactly clear on what an IT of 1: 1 is achieving, and signal levels being carried:
What is the difference in signal level from say 45 tube > IT, compared to say IT > 845's?
The 45 PS is IIRC 330 volts. Why *not? run from the 45 PS, an umbilical (rated say 500 volts) to the IT on the 845's chassis, where it can be used by alternative suitable drivers?
The IT for must handle the 45 (I have the Bugle parts); how do you determine what drivers into an 845 an IT can do, and the sweetspot?
Just checking: no ITs have multiple taps, allowing different bias currents hence and maybe different tubes??
Beginning to look like one IT to cover the 45/ 47/ 6w6/ EL34.
Could the EP 3033 do all these?
FYI I believe James are very good, often best value, specs: www.thlaudio.com/jamesxformer.htm ~ a good option there?
Thanks
Not being exactly clear on what an IT of 1: 1 is achieving, and signal levels being carried:
What is the difference in signal level from say 45 tube > IT, compared to say IT > 845's?
The 45 PS is IIRC 330 volts. Why *not? run from the 45 PS, an umbilical (rated say 500 volts) to the IT on the 845's chassis, where it can be used by alternative suitable drivers?
The IT for must handle the 45 (I have the Bugle parts); how do you determine what drivers into an 845 an IT can do, and the sweetspot?
Just checking: no ITs have multiple taps, allowing different bias currents hence and maybe different tubes??
Beginning to look like one IT to cover the 45/ 47/ 6w6/ EL34.
Could the EP 3033 do all these?
FYI I believe James are very good, often best value, specs: www.thlaudio.com/jamesxformer.htm ~ a good option there?
Thanks
Hi
I just tried to find a decent swap-in tube in lieu of a 45, to try in a Bugle amp with minimal changes, to drive an 845 amp. Zero success. : (
Looks like a separate driver circuit entirely.
If the IT really needs to sit in the 45 Bugle case, and no other tube easily swaps in: maybe do not select an IT on the basis of a larger sweet spot.
Though It may have other advantages:
Some ITs (ElectraPrint, Nicholas) are wound bi-filar - is that an advantage?
(Apart from cost) how else do you select a 1:1 IT? 😕
Thanks
I just tried to find a decent swap-in tube in lieu of a 45, to try in a Bugle amp with minimal changes, to drive an 845 amp. Zero success. : (
Looks like a separate driver circuit entirely.
If the IT really needs to sit in the 45 Bugle case, and no other tube easily swaps in: maybe do not select an IT on the basis of a larger sweet spot.
Though It may have other advantages:
Some ITs (ElectraPrint, Nicholas) are wound bi-filar - is that an advantage?
(Apart from cost) how else do you select a 1:1 IT? 😕
Thanks
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