navin,
an EI-150 core stacked to 2inch is good for this amp, this core have a center leg of 1.5 inches. you can even go 3inch stack height if you like. later on you can still use the traffo for 6550 amps.
an EI-150 core stacked to 2inch is good for this amp, this core have a center leg of 1.5 inches. you can even go 3inch stack height if you like. later on you can still use the traffo for 6550 amps.
cogsncogs said:
thanks wayne. now to integrate this into the schematic you posted earlier.
BTW sorry for the delay in my responses but we had a very very close friend (she was also my wife's soul mate and best friend) pass away on thursday afternoon and we have been over at her mom's place heling her cope with the loss of her only daughter.
Tony said:
Thanks I will pass this to the guy who is making my tranny. Right now I am looking for someone who can make me a torroid tranny to save space and weight.
cogsncogs said:
Long time no see...
I have since scrapped that one. I did a new design last year using differential stages all the way.
My new design
Bias is set to 2x40mA and optimal primary impedance around 5800-6600 ohms with 43% taps. Feedback 21dB. The reason for the lowish 400V feed is the power iron, Hammond 372JX (300-0-300V). Output power 30W. I could have used a CCS on the second stage but didn't. The amp is remarkably free from hum.
The old now scrapped design is here:
Old design
Jax said:
care to detail why you decided to use diffrential stage all the way?
What are the advantages at the cost of 1/2 6SL7 per channel.
Tony: I was lazy 
Anyway, it's not really necessary if the halves of the 6SN7 are reasonably matched. You will adjust total DC balance with the pot on the input stage anyway.
navin: Main reason is that I wanted to get rid of as many electrolytic capacitors as possible and thus keeping the number of low frequency poles down to a minimum. Second reason is the power supply rejection ability of a differential pair. Tradeoff is gain but the amp has enough gain to allow over 20dB feedback and still be able to play directly from a CD player (replace input resistor with a 100k pot).
Anyway, it's not really necessary if the halves of the 6SN7 are reasonably matched. You will adjust total DC balance with the pot on the input stage anyway.navin: Main reason is that I wanted to get rid of as many electrolytic capacitors as possible and thus keeping the number of low frequency poles down to a minimum. Second reason is the power supply rejection ability of a differential pair. Tradeoff is gain but the amp has enough gain to allow over 20dB feedback and still be able to play directly from a CD player (replace input resistor with a 100k pot).
sAmE hErE! 😀
@navin, you still have the power supply to figure out!
If you haven't already, go here and download yourself a copy
http://www.duncanamps.com/psud2/index.html
of Duncan's pwr supply designer. Indispensable, a must have!
On the subject of pwr tranny's IMO a good secondary set up would be:
1) 370VAC HT w/ taps @10 or 15V apart, say 340, 350, 360 etc.
340-350VAC approx. is what you will need, depending on how much current you will be pulling from it and the source impedance of the tranny. This is where Duncan's PSUD comes in handy. So you will need to figure this out before you order. I have no idea what the source imp. of my tranny is, but it is rated @500mA. One big pwr tranny!
2) 6.3VAC CT for EL34 heaters (mine has no CT)
1) 6.3VAC CT for Input/Driver heaters (I run mine DC)
1) 60-70VAC for output tube bias
Some regulate the bias supply when they shouldn't. One good reason not to is that the bias supply will follow the HT supply, say during mains supply fluctuation. The only time to regulate the bias supply is if the HT is regulated also, esp. the screen supply when operated in 'pentode' mode.
IMO I would say it's best to over-design the power supply a little! 😉 This is an area where a lot of manufactures 'skimp', go the cheap route and turn an otherwise good amplifier design into a bad one!
So a little over-kill here is a good thing!
Sorry to hear about things on your end. 🙁
Wayne
how about a 12at7 - 6cg7/6fq7 instead of the 6sl7/6sn7 combo?
do octals really lord it over miniatures when it comes to peformance?
do octals really lord it over miniatures when it comes to peformance?
In my all-differential design, I use a step network between 6SL7 LTP splitter and 6SN7 differential driver, instead of direct
coupling. This is where my design diverges a little from that of Thorsten Loesh.
The advantages of a step network over direct doupling include:
* A much lower grid voltage on the 6SN7 (could be 50v or less), allowing more suitable operating points to be used for both
6SL7 and 6SN7, in terms of plate load resistor, plate-cathode voltage and plate current.
* Amplification of any DC imbalance in the 6SL7 is much less. DC coupling can cause a serious DC offset.
The coupling capacitor in a step network can be included in a NFB loop without incurring LF instability, which is the most common
objective of using DC coupling in the first place.
The downside of a step network approach, of course, is the cost of a few additional components, namely, 2 grid "leak" resistors, 2 coupling capacitors and two coupling bypass resistors - not a big price to pay, IMHO, for considerably easier design and superior balance.
coupling. This is where my design diverges a little from that of Thorsten Loesh.
The advantages of a step network over direct doupling include:
* A much lower grid voltage on the 6SN7 (could be 50v or less), allowing more suitable operating points to be used for both
6SL7 and 6SN7, in terms of plate load resistor, plate-cathode voltage and plate current.
* Amplification of any DC imbalance in the 6SL7 is much less. DC coupling can cause a serious DC offset.
The coupling capacitor in a step network can be included in a NFB loop without incurring LF instability, which is the most common
objective of using DC coupling in the first place.
The downside of a step network approach, of course, is the cost of a few additional components, namely, 2 grid "leak" resistors, 2 coupling capacitors and two coupling bypass resistors - not a big price to pay, IMHO, for considerably easier design and superior balance.
No, you're confused. I'm talking about the difference between DC coupling and step coupling. In both cases, the 6SL7 LTP is the first stage, using both halves.
I cannot, for the life of me, understand why you think that saving 1/2 of a 6SL7, by using a single-ended input stage instead of differential, is such a big deal. What are you going to use the "saved" 1/2 for? Paralleling, possibly, to reduce tube noise? Or are you thinking of using 1/2 in each channel, with the attendant risk of cross-talk? In either case, PSRR will be poor compared with a differential design.
I cannot, for the life of me, understand why you think that saving 1/2 of a 6SL7, by using a single-ended input stage instead of differential, is such a big deal. What are you going to use the "saved" 1/2 for? Paralleling, possibly, to reduce tube noise? Or are you thinking of using 1/2 in each channel, with the attendant risk of cross-talk? In either case, PSRR will be poor compared with a differential design.
ray_moth said:
Oh the main reason I am sharing 1 6SL7 between 2 channels is because i dont have enough 6SL7. Even the one I am getting is gifted.
Are the risks of cros talk that high?
Good idea. I'll try it out in my design. The openloop gain will go down a bit though.
I have never seen Loesch's design.
Tony said:
In my opinion and experience: No. The 6SL7 has an even lower Pa than 12AT7, but 6SN7 Pa is higher, where that is of consequence. Sensitivity to shock and microphony should be better with miniatures.
One respects those who claim to perceive audible differences, but that is such a subjective and circuit dependant thing that one does not want to step on a nerve. There is also availability. But I did occasionally use the bigger bottles for aesthetic reasons - the originals had them so the customer wanted them!
Regards
Hi,
Would those 0.25W Bournes trimpots work for bias and dc balance adjustment purposes? Or should I still get those 5W ww pots? If grid current is low then this could work?
My only reason is to save some real state inside the chassis because those Bournes trimpots are kinda small and I think of fixing them in a pcb.
Thanks!
Would those 0.25W Bournes trimpots work for bias and dc balance adjustment purposes? Or should I still get those 5W ww pots? If grid current is low then this could work?
My only reason is to save some real state inside the chassis because those Bournes trimpots are kinda small and I think of fixing them in a pcb.
Thanks!
I'm using these trimmers in my amplifier for both balancing and bias:
It's #67 in the list, ½W 20 turn.
http://www.bitechnologies.com/products/multi_trim.htm
It's #67 in the list, ½W 20 turn.
http://www.bitechnologies.com/products/multi_trim.htm
Hi Jax,
I have a bunch of those typical #3306 Bournes I use in ss amps but maybe the cermet and multiturn ones are better in this application.
Thanks!
I have a bunch of those typical #3306 Bournes I use in ss amps but maybe the cermet and multiturn ones are better in this application.
Thanks!
Johan Potgieter said:
thanks, and i thought these miniatures are an improvement as far as space reduction is concerned without giving away sonic qualities, but then its just me.
- Status
- Not open for further replies.