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Old 25th May 2006, 12:22 PM   #1
jim is offline jim  Belgium
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Default What tube instead of 7189

Hi All,

I've got a pair of output transformers of an old Pioneer SM83 amplifier.
I would like to use 'm with another tube than the 7189 (or EL84M) they were designed for.
The PP-7189 delivers 18W at 400V so I think I can use some beefier tubes than the EL84.

Any suggestions? 6L6 - 807 ???

Thanks,
Jim
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Old 25th May 2006, 12:27 PM   #2
SY is offline SY  United States
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7591 or 6L6.
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Old 27th May 2006, 12:00 AM   #3
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Hi jim ,

First of all , you have to say if the output transformers are wound for
UL operation ( 5 primary taps ) or for Pentode operation ( 3 primary taps ) , because the impedance plate to plate , are very different case
to case ( aprox. 40% ) .

If you know how to do it , calculate the TURNS RATIO : Primary plate to
plate versus secondary 8 ohms output and report the values .

Then we can recommend the best replacement .

Regards ,

Carlos
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Old 27th May 2006, 08:24 AM   #4
jim is offline jim  Belgium
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Carlos,

Transformers are for pentode-mode only.
Raa = 8k.

Greetz,
Jim
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Old 27th May 2006, 08:13 PM   #5
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Since you have 18W xfmrs with an Raa= 8.0K, these would be ideal for use with 6V6s.

Operate Class AB1, Vpp= 285Vdc, Ip= 70mA, Vgk= -19Vdc. This will give 14W with 3.5% THD before adding feedback. Add local feedback + gNFB and that would perform quite well. 6V6s get considerable praise for sonic excellence.
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Old 27th May 2006, 10:23 PM   #6
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It may be possible to run these at a higher voltage and power, but the low end will likely suffer from transfomer saturation. It's always OK (and usually better) to run at lower power.
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Old 28th May 2006, 07:57 PM   #7
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Hi JIM ,

First of all , I think that there is a little mistake , because 7189’s , connected as push-pull pentodes , with +B 400 V , and loaded
with 8000 ohms plate to plate , can deliver more than 25 Watts ,
with 4% THD , and not “only” 18 Watts , as you said .

So I think that , your output tranny can “hand” more than 24 Watts , without core saturation.

I’ll gave to you many suggestions , as follows :

6V6 – 1% THD
PP – Class AB1 – 12 Watts
Plate voltage : 350 VDC Screen voltage : 340 VDC
Max. at each grid control : 13 Volts RMS ( signal level )
COMMON cathode resistor : 250 ohms x 10 Watts

6973 – 2% THD
PP – Class AB – 24 Watts
Plate voltage : 400 VDC Screen voltage : 290 VDC
Control grid : ( - ) 25 VDC
Fixed bias

6BQ5 / EL84 – 4% THD
PP – Class AB1 – 17 Watts
Plate voltage : 300 VDC Screen voltage : 290 VDC
Max. at each grid control : 10 Volts RMS ( signal level )
COMMON cathode resistor : 130 ohms x 15 Watts

6CZ5 – 1% THD
PP – Class AB1 – 22 watts
Plate voltage : 350 VDC Screen voltage : 280 VDC
Control grid : ( - ) 23.5 VDC
Fixed bias

6L6 GB / GC / WXT , etc. – 2% THD
PP – Class AB1 – about 24 Watts
Plate voltage : 360 VDC Screen voltage : 270 VDC
Control Grid : ( - ) 22.5 VDC
Fixed bias
Note : In this case , the ideal load would be 6600–7000 ohms plate to plate , but 8000 ohms still works too .

Note 1 : The values of THD ( harmonic distortion ) are without
negative feedback , with NFB , the values will lower 10
times or more .

Note 2 : KT66 , 7591 , 807 and 5881 , need to be running under
Ultra Linear operation condition , to be loading with
8000 ohms plate to plate .

Note 3 : 6CA7 / EL34 can deliver more than 25 Watts , so , your
output tranny , will have core saturation and distortion.

Any doubt , feel free to ask ,

Regards ,

Carlos
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Old 28th May 2006, 08:27 PM   #8
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Quote:
Originally posted by refference


6L6 GB / GC / WXT , etc. – 2% THD
PP – Class AB1 – about 24 Watts
Plate voltage : 360 VDC Screen voltage : 270 VDC
Control Grid : ( - ) 22.5 VDC
Fixed bias
Note : In this case , the ideal load would be 6600–7000 ohms plate to plate , but 8000 ohms still works too .


Note 2 : KT66 , 7591 , 807 and 5881 , need to be running under
Ultra Linear operation condition , to be loading with
8000 ohms plate to plate .
How do you figure this? The 807 and 6L6 are the same VT in different bottles. Same Q Points and everything. The 807/6L6 are not good for ultralinear (which I don't like anyway) since this VT was intended to run with Vpp up and Vsgsg held down. You don't get much with them in ultralinear (~10W). You bust the R(L) spec that much, and you aren't going to get ~2.0% THD anymore.
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Old 29th May 2006, 03:42 AM   #9
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Hi JIM ,

First of all I want to say to Miles Prower , that 6L6 and 807
“ARE NOT THE SAME TUBE IN DIFFERENT BOTTLES”

They have some common characteristics , but you NEVER
can say that they are “the same tube” , as you said .

Second :
I NEVER affirmed on my previous post , that 6L6 and 807
are good tubes for UL operation , you did not understand .
What I had said , was the following :

“The 807 and others , MUST to be in a UL circuit , to work fine
with a load of 8000 ohms , ” ( 8000 ohms is the input impedance
plate to plate of JIM’s output tranny , and as he said it is only for
pentode connection , then , 807 and others , are not useful tubes
for him )

JIM ,
All technical characteristcs and suggestions that I had sent
on my previous post , has like base , the following bibliography ;

RCA 28 – Receiving Tube Manual
SYLVANIA – Technical Manual - 1954 Edition / 1958 Edition and
1970 Edition
Radio Amateur’s Handbook – 1939 Edition and 1952 Edition

Regards ,

Carlos
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Old 29th May 2006, 05:15 AM   #10
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Quote:
Originally posted by refference
[B]Hi JIM ,

First of all I want to say to Miles Prower , that 6L6 and 807
“ARE NOT THE SAME TUBE IN DIFFERENT BOTTLES”

They have some common characteristics , but you NEVER
can say that they are “the same tube” , as you said .
Not just "some common characteristics", but identical Q Points, power out, and THD figures. In another thread, Tubelab said he took apart both types and found no internal difference. Just a couple of nights ago, I also found a schematic for a CW xmtr that used a 6L6 as the final in a circuit identical to one used for 807s.

Quote:
Second :
I NEVER affirmed on my previous post , that 6L6 and 807
are good tubes for UL operation , you did not understand .
What I had said , was the following :

“The 807 and others , MUST to be in a UL circuit , to work fine
with a load of 8000 ohms , ” ( 8000 ohms is the input impedance
plate to plate of JIM’s output tranny , and as he said it is only for
pentode connection , then , 807 and others , are not useful tubes
for him )
You also said:
Quote:

6L6 GB / GC / WXT , etc. : 2% THD
PP : Class AB1 : about 24 Watts
Plate voltage : 360 VDC Screen voltage : 270 VDC
Control Grid : ( - ) 22.5 VDC
Fixed bias
Note : In this case , the ideal load would be 6600 -- 7000 ohms plate to plate , but 8000 ohms still works too .
Not word one there about UL, implying that he could use the 6L6, but not the 807.
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