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Spring time

79.36.208.109
Posted on May 16, 2015 at 02:44:54
6AS7_6SN7



When warm season arrives it's time to put in line the less 'heat wasting' amplifiers (a couple of all triode & tetrode ones, just for sake of completeness).

 

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RE: Spring time, posted on May 16, 2015 at 17:39:24
Triode_Kingdom
Audiophile

Posts: 10044
Location: Central Texas
Joined: September 24, 2006
 Is that bottom amplifier push-pull AB1? If so, I would like to know more about the circuit details and any electrical measurements you've made. Very nice looking gear, all of it!



 

RE: Spring time, posted on May 17, 2015 at 04:40:52
6AS7_6SN7
 Yes it is. You are very welcome.

http://db.audioasylum.com/mhtml/m.html?forum=tubediy&n=190082&highlight=6as7_6SN7&r=&search_url=%2Fcgi%2Fsearch.mpl%3Fforum%3Dvintage%26searchtext%3Dbozak

http://db.audioasylum.com/mhtml/m.html?forum=tubediy&n=190185&highlight=6as7_6SN7&search_url=%2Fcgi%2Fsearch.mpl%3Fforum%3Dvintage%26searchtext%3Dbozak

http://db.audioasylum.com/mhtml/m.html?forum=tubediy&n=203486&highlight=6as7_6sn7+12AT7+829B&r=&search_url=%2Fcgi%2Fsearch.mpl%3Fsearchtext%3DRed%2Brose%2BRosette%2B2%26b%3D-1

http://db.audioasylum.com/mhtml/m.html?forum=tubediy&n=203739&highlight=6as7_6sn7+12AT7+829B&search_url=%2Fcgi%2Fsearch.mpl%3Fsearchtext%3DRed%2Brose%2BRosette%2B2%26b%3D-1

Luca

 

RE: Spring time, posted on May 19, 2015 at 05:46:02
Triode_Kingdom
Audiophile

Posts: 10044
Location: Central Texas
Joined: September 24, 2006
 Thanks for the links. Unfortunately, I can't read most of the text. What value did you use for the output transformers (plate-to-plate Z)? I seem to remember that these tubes might need about 6K-7K when operated with two in parallel.

 

RE: Spring time, posted on May 19, 2015 at 11:40:22
andy evans
Audiophile

Posts: 4378
Joined: October 20, 2000
 But is it winter for Poland and France?

 

RE: Spring time, posted on May 19, 2015 at 12:39:45
6AS7_6SN7
 In Rome (ITALY) the maximum temperature (more often than not) already exceeds 30 °C.
I would say it's regular spring season.



 

RE: Spring time, posted on May 19, 2015 at 12:55:44
6AS7_6SN7
 In order to make a long story short, I used the same 2X115V-2X6V 50Hz/50W toroidal power transformers.
In the case of one GI-30 tube per channel (or GI-30/829B/7E29), one 50W toroidal transformer per channel.
In case of two GI-30 parallel tubes per channel, two toroidal 50W transformers per channel.

I hope this (and the schematics) will suffice to get the message.

 

RE: Spring time, posted on May 19, 2015 at 14:18:18
Triode_Kingdom
Audiophile

Posts: 10044
Location: Central Texas
Joined: September 24, 2006
 I'm having difficulty putting it together. What is the winding ratio from the anodes to the load, and what is the load Z?

 

RE: Spring time, posted on May 19, 2015 at 15:44:18
andy evans
Audiophile

Posts: 4378
Joined: October 20, 2000
 It's part of the lyrics of this, from the cult film "The Producers":

https://www.youtube.com/watch?v=kHmYIo7bcUw

 

About 6.1 K @ 8 Ohm is the answer (LTSpice confirmed), posted on May 20, 2015 at 01:17:57
6AS7_6SN7



With reference to the enlarged picture:

Transformers 2X110V/2X6V 50W-50Hz (toroids): T1, T2

Primary T1: L12, L13
Primary T2: L10, L8
Secondary T1: L15, L14
Secondary T2: L11, L9

Wound up auxiliary (manually added) for NFB: T1 L17, T2 L16
[voltage ratio of each auxiliary winding = 110/9 = 12.2 = SQRT (6/0.04)]

In sim world (within class A operation and with NFB), 140V of plate voltage variation corresponds to 23 mA of current variation (140/0.023 = 6086 Ohm).

The basic plate impedance corresponding to 110/6 V ratio (@ 8 Ohm load) is (110/6)*(110/6)*8 = 2688 Ohm.

As T1 and T2 primaries are in series, the theoretical impedance would be 5.4K, which is consistent with the above 6.1K 'measured' in sim world when NFB is applied.








 

RE: Spring time, posted on May 20, 2015 at 12:27:42
Frihed89
Audiophile

Posts: 15703
Location: Copenhagen
Joined: March 21, 2005
 You could write a hit country song about the bad weather up here in Denmark.
The "green winter" has just begun in May. I'm heating my summer cottage with 2 class A amps at the same time!

 

RE: About 6.1 K @ 8 Ohm is the answer (LTSpice confirmed), posted on May 20, 2015 at 20:51:14
Triode_Kingdom
Audiophile

Posts: 10044
Location: Central Texas
Joined: September 24, 2006
 Thanks, that's in line with my estimate for a PP pair. I think these are capable of roughly 80-100W output in AB1. Someday I'll get everything together for my own version of this... :)

 

Another picture from the past.., posted on May 22, 2015 at 01:27:57
6AS7_6SN7
 In this picture the auxiliary windings for NFB can be seen.
I made those windings because the 560V HT comes from direct 220V AC line rectification.

http://db.audioasylum.com/mhtml/m.html?forum=tubediy&n=190208&highlight=construction+hints+6AS7_6SN7&search_url=%2Fcgi%2Fsearch.mpl%3Fauthor%3DSal%26user_id%3D6472%26forum%3DALL%26sortRank%3DNone%26sort%3Ddate%26sortOrder%3DDESC

 

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