2359glenn | studio

[2359glenn]

 

  1956, nice gibosi.
 
I love the fact that I can listen to Glenn's OTL  with tubes older than I am 

.

 
Well, I am sad to say that these tubes are not older than I am...
 
Oh well... lol...  
 
Anyway, first impressions, the Tungsram PV 200/600 sounds very good and I paid only $35.
 

 
Oh, the little red wire off to the right allows me to measure B+. And if my calculations are correct, in this configuration, that is, running four 6BX7 in a Glenn OTL, the PV 200/600 has a voltage drop of 27.

See what what the voltage drop is with 6AS7s as outputs?

 

[gibosi]

  See what what the voltage drop is with 6AS7s as outputs?

 
Unfortunately for comparison purposes, the PV 200/600 can provide at most 200ma, and as it is my understanding that the 6AS7/6SN7 configuration requires at least 220ma, I did not think it wise to use it with a pair of 6AS7.
 
However, I did compare the HEXFRED to my three reference tube rectifiers, a Cossor 53KU, a GEC U18/20 and a Philips/Sittard GZ34. And the results are very interesting, I think....
 

	Four 6BX7 (B+ = 323)		Two 6AS7 (B+ = 257)
Rectifier	Measurement	Vdrop	Measurement	Vdrop
HEXFRED	322	1	256	1
53KU	303	20	234	22
U18/20	292	31	224	33
GZ34	315	8	244	13

 
The procedure, for those who might be interested.
 
In Glenn's design, the true B+ can be found on pin-2 of any output tube. So in this way, for each rectifier, I measured true B+. Next, in order to calculate voltage drop, it is necessary to subtract the true B+ from the potential B+, that is, the value of B+ before the voltage drop. The easiest way to obtain this value is to use the HEXFRED. We know that the HEXFRED has a voltage drop of 1. So adding 1 to the measured value should equal the potential B+. (I am not at all sure of my terminology here, but I hope this clear.)
 
As the four 6BX7 configuration requires considerably less current than the 6AS7, that is 140ma versus 220ma, we can see the relationship between total current draw and B+. And fortunately, the 6BX7 can easily handle more than 300 volts, so no harm.

 
What I found most interesting is that the voltage drop of the 53KU and U18/20 changed very little, relatively speaking, compared to the GZ34, when switching from 6BX7 to 6AS7, But unfortunately, I have no idea why this is so.

 

[gibosi]

While I had a pair of 6AS7 installed, decided to measure a few more rectifiers... 
 
(Sorry for the lousy formatting... Too lazy to insert and fill out a table.... lol
 
With two 6AS7G
B+ = 257VDC
 
Rectifier                                        Measurement    VDrop
 
HEXFRED    Glenn                          256VDC             1VDC
GZ34 Sittard                                  244VDC           13VDC
53KU Cossor                                 234VDC            22VDC
U18/20 GEC                                  224VDC            33VDC
5Z3PA                                           221VDC           36VDC
FW4-500 Mullard                            222VDC            35VDC
AZ50 Eindhoven                            222VDC            35VDC
FW4-500   Tungsram                     222VDC            35VDC
GZ37 Mullard                                230VDC            27VDC
3DG4                                           240VDC            17VDC
GZ32                                           237VDC             20VDC    

 

[2359glenn]

  While I had a pair of 6AS7 installed, decided to measure a few more rectifiers... 
 
(Sorry for the lousy formatting... Too lazy to insert and fill out a table.... lol
 
With two 6AS7G
B+ = 257VDC
 
Rectifier                                        Measurement    VDrop
 
HEXFRED    Glenn                          256VDC             1VDC
GZ34 Sittard                                  244VDC           13VDC
53KU Cossor                                 234VDC            22VDC
U18/20 GEC                                  224VDC            33VDC
5Z3PA                                           221VDC           36VDC
FW4-500 Mullard                            222VDC            35VDC
AZ50 Eindhoven                            222VDC            35VDC
FW4-500   Tungsram                     222VDC            35VDC
GZ37 Mullard                                230VDC            27VDC
3DG4                                           240VDC            17VDC
GZ32                                           237VDC             20VDC    

Looks like the GZ34 and 3DG4 are the best tubes

 

[leftside]

No wonder the GZ34 metal base are so popular. 

 

[2359glenn]

  While I had a pair of 6AS7 installed, decided to measure a few more rectifiers... 
 
(Sorry for the lousy formatting... Too lazy to insert and fill out a table.... lol
 
With two 6AS7G
B+ = 257VDC
 
Rectifier                                        Measurement    VDrop
 
HEXFRED    Glenn                          256VDC             1VDC
GZ34 Sittard                                  244VDC           13VDC
53KU Cossor                                 234VDC            22VDC
U18/20 GEC                                  224VDC            33VDC
5Z3PA                                           221VDC           36VDC
FW4-500 Mullard                            222VDC            35VDC
AZ50 Eindhoven                            222VDC            35VDC
FW4-500   Tungsram                     222VDC            35VDC
GZ37 Mullard                                230VDC            27VDC
3DG4                                           240VDC            17VDC
GZ32                                           237VDC             20VDC    

The transformer for the OTL was chosen to use the 3DG4. Low voltage drop and can handle 350ma plus I could buy
them for $1.  The proper voltage for a 6AS7 is 120 with the 2 1/2s hooked in series each one gets 120 volts.
The filament winding was chosen 0>3.3>5 so 5volt rectifiers can be used too.
I don't feel any of these expensive rectifiers sound better then the 3DG4 and can't believe people spend $1000
for TAK 274B rectifiers craziness.
Have to be careful using some of these tubes if running 6336 tubes in 5998 mode as the current will go way up.
OTL amps using the Lundahl power transformer and PY500 rectifiers can handle 1amp or 1000ma. 

 

[whirlwind]

When I first ordered my amp, I remember you suggesting the 3DG4 to me Glenn, so I bought one....then I changed my mind and decided to go with the PY500 rectifiers.
 
If I am not mistaken the tube to the right in this picture is a 3DG4, the one with the angled plates.
 

 

[2359glenn]

  When I first ordered my amp, I remember you suggesting the 3DG4 to me Glenn, so I bought one....then I changed my mind and decided to go with the PY500 rectifiers.
 
If I am not mistaken the tube to the right in this picture is a 3DG4, the one with the angled plates.
 

That is a 5AW4 it can handle 250ma it is another good one to use in the OTL.
Not for you though.

 

[whirlwind]

Thanks for the clarification Glenn....I know that I can not use it.
 
If you want it Ken, shoot me a pm and I will send it your way.

 

[gibosi]

  Thanks for the clarification Glenn....I know that I can not use it.
 
If you want it Ken, shoot me a pm and I will send it your way.

 
I already have a couple of 5AW4 so I am good. But thanks!
 
And this reminds me that I forgot to measure the 5AW4, 5R4GY and VU71. I also have a few others, the 5U4G, 1861 and 1815, but they cannot provide enough current for a pair of 6AS7...

 

[gibosi]

Updated to include all the rectifiers in my possession that can provide at least 250ma and are thus suitable for use with a pair of 6AS7. I also have a Mullard GZ33, but it is out on loan to a friend.
 
Edit: Oh, I also have an AX50 which is a mercury-vapor rectifier. But as it has a tendency to arc, I don't use it...
 
In terms of voltage drop, the best rectifiers are the GZ34, 3DG4, GZ32 and 53KU. Of these, I prefer the sound of the 53KU and GZ34. But of course, YMMV.
 
With two 6AS7G
B+ = 257VDC
 
Rectifier                                        Measurement    VDrop

HEXFRED Glenn                                256VDC          1VDC
GZ34 Sittard                                    244VDC        13VDC
53KU Cossor                                    234VDC        22VDC
U18/20 GEC                                     224VDC        33VDC
5Z3PA Shuguang                              221VDC        36VDC
FW4-500 Mullard                              222VDC        35VDC
AZ50 Eindhoven                               222VDC        35VDC
FW4-500 Tungsram                          222VDC        35VDC
GZ37 Mullard                                  230VDC        27VDC
3DG4 Tung Sol                                240VDC        17VDC
GZ32 Mullard                                  237VDC        20VDC
VU71 Canadian Westinghouse            227VDC        30VDC
5R4GY RCA                                    219VDC        38VDC
5AW4 ? labeled CBS Hytron              229VDC        29VDC

 

[whirlwind]

Great work Ken.

 

[raybone0566]

Know how you guys like to post some food pics, so here's a few Labor Day southern style meal

 

[2359glenn]

Know how you guys like to post some food pics, so here's a few Labor Day southern style meal

It's been awhile since there was some good food pictures.   Looks familiar being I live in the South
Good going.
I will have to take some to post.

 

[Xcalibur255]

  Updated to include all the rectifiers in my possession that can provide at least 250ma and are thus suitable for use with a pair of 6AS7. I also have a Mullard GZ33, but it is out on loan to a friend.
 
Edit: Oh, I also have an AX50 which is a mercury-vapor rectifier. But as it has a tendency to arc, I don't use it...
 
In terms of voltage drop, the best rectifiers are the GZ34, 3DG4, GZ32 and 53KU. Of these, I prefer the sound of the 53KU and GZ34. But of course, YMMV.
 
With two 6AS7G
B+ = 257VDC
 
Rectifier                                        Measurement    VDrop

HEXFRED Glenn                                256VDC          1VDC
GZ34 Sittard                                    244VDC        13VDC
53KU Cossor                                    234VDC        22VDC
U18/20 GEC                                     224VDC        33VDC
5Z3PA Shuguang                              221VDC        36VDC
FW4-500 Mullard                              222VDC        35VDC
AZ50 Eindhoven                               222VDC        35VDC
FW4-500 Tungsram                          222VDC        35VDC
GZ37 Mullard                                  230VDC        27VDC
3DG4 Tung Sol                                240VDC        17VDC
GZ32 Mullard                                  237VDC        20VDC
VU71 Canadian Westinghouse            227VDC        30VDC
5R4GY RCA                                    219VDC        38VDC
5AW4 ? labeled CBS Hytron              229VDC        29VDC

Yeoman's work right here.  Very nice.
 
I'd suggest adding a garden variety 5U4G and 5U4GB (any USA brand) to serve as a comparative basis against the other tubes since it is used so commonly by so many people.
 
I can't say I was surprised to see the 5R4GY have the biggest drop.  I think this tube sounds very lovely in applications where the B+ requirement of the circuit is very low (I'm subbing one in place of what is supposed to be a 5Y3 in my Inspire), but in amps with higher requirements it's just too soft.