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6SJ7 AND 6SS7 ?
11/23/2010 6:15:30 AMChris
Hello all. Can a 6SS7 be used as a substitute for a 6SJ7 or could this be hazardous??Thanks for info
11/23/2010 10:15:33 AMJohnnysan
:Hello all. Can a 6SS7 be used as a substitute for a 6SJ7 or could this be hazardous??Thanks for info
:
They have the same basing, but are not listed as substititutes. I doubt if it would be hazardous, but it may not work properly.
Johnnysan-



11/23/2010 1:25:36 PMMikeStop
Here's a list of possible substitutes.
http://www.nostalgiaair.org/tubes/6ss7.htm
11/23/2010 1:28:41 PMMikeStop
Sorry, this is the link I meant to foward!
http://www.nostalgiaair.org/tubes/6sj7.htm
11/23/2010 1:47:04 PMThomas Dermody
The 6SS7 and 6SJ7 are listed on this site (and most likely in any tube manual) as remote cut-off and sharp cut-off respectively. This means that the first one will most likely have less gain than the second, but is more likely to be better suited for AVC controlled circuits. The second may or may not introduce distortion because of the presence of or lack of AVC voltage, depending on signal strength and depending on its biasing preferences. Often enough tubes of this kind work well in a remote cut-off preferred circuit, and the only difference is the increased gain.

I do not know the specifics of these tubes other than what I have given above, since I have not consulted my tube manual, even though it is in the other room. Most likely maximum voltage ratings will be similar for the two tubes, but you should consult your manual to be sure, and to be sure that you won't exceed the rated maximum if that is possible. Also, most likely both tubes contain a 6.3 volt filament. However, if they are going to be used in a series string arrangement, it should be known whether or not they both consume the same amount of current. More current will cause the tube to fail to light, and less current will cause the tube to glow too brightly, and possibly burn out. For parallel operation, small differences in current draw are of no concern, and should only be of concern when the difference is great and there is a chance of excessive current draw from the power transformer. Since either both of these tubes draws .3 amperes, or one draws .150 and one .3, there is almost no concern for excessive current draw.

T.

11/23/2010 1:51:58 PMThomas Dermody
Remote cut-off designed tubes have varied spacing control grid windings to allow for gain control. As negative bias is increased, part of the grid area runs into cut-off, thereby reducing effective current flow from a portion of the cathode. However, due to varied control grid spacing, part of the grid will still function normally, and not run in cut-off.

Sharp cut-off designed tubes have uniformly spaced control grid windings. As negative bias is increased, the entire grid runs into the cut-off region. This may introduce distortion in some circuits, and cause early detection of radio signals.

The mixing of these two kinds of tubes is most critical in grid leak and square plate detector circuits, and is less of a concern for pure RF amplification circuits, though trouble can be caused here, too, by the insertion of the wrong kind of tube. Usually no physical harm is done, but performance may suffer.

....Try the swap and see if you like it.

T.

11/23/2010 4:39:30 PMWalter
I have communications receivers that use the 6SS7 for RF/IF amp circuits.
I really didn't notice any performance differences between the 2 tubes(my tin ear), but do I prefer using the tube that was specified for the supporting circuit's characteristics.
11/23/2010 4:55:40 PMThomas Dermody
You would notice the difference the most on weak stations. The tube with more gain might pull in the weak stations more strongly. With strong signals, the two tubes might perform similarly due to AVC action, if used in an AVC controlled circuit.

T.

11/23/2010 6:56:00 PMPeter G Balazsy
6SS7 = 150 ma
6SJ7 = 300 ma
11/23/2010 7:01:08 PMJohnnysan
:6SS7 = 150 ma
:6SJ7 = 300 ma
:
Peter is right; I didn't even think of the filamnet current ratings. If the tubes are series filament connected it won't work properly.
Johnnysan-



11/23/2010 11:18:38 PMPeter G Balazsy
Yeah... typically I see the 6SS7 used in AA6 sets where in the normal AA5 set you'll see:
12SA7, 12SK7, 12SQ7, 50L6, 35Z5 .

But in an AA6 you may see the 1st and 3rd tubes are 6SS7

Like the Farnsworth model ET066:
it uses:
6SS7 12SA7 6SS7 12SQ7 50L6 35Z5

11/24/2010 4:59:16 AMChris
:Hello all. Can a 6SS7 be used as a substitute for a 6SJ7 or could this be hazardous??Thanks for info
:Thankyou gentlemen for this information
11/24/2010 8:50:20 AMChris
::Hello all. Can a 6SS7 be used as a substitute for a 6SJ7 or could this be hazardous??Thanks for info
::Thankyou gentlemen for this information
:The 6SJ7 just arrived in the mail, so I put it in place of the 6SS7 and BOOM the volume jumped to life ,so must be the double current draw of the filament!
11/24/2010 2:02:52 PMcodefox
The very common 6SK7 could also be subbed here too as it is a remote cutoff pentode (filament current notwithstanding.) All 3 of 'em work just fine at sub R.F. frequencies, and for sure in most audio applications.

:::Hello all. Can a 6SS7 be used as a substitute for a 6SJ7 or could this be hazardous??Thanks for info
:::Thankyou gentlemen for this information
::The 6SJ7 just arrived in the mail, so I put it in place of the 6SS7 and BOOM the volume jumped to life ,so must be the double current draw of the filament!
:

11/25/2010 12:08:41 AMThomas Dermody
The reason why your amp got louder isn't because of difference in filament current, but rather the difference in gain. I explained this in more detail earlier.

Filament current affects tube gain little in most cases, so long as the voltage across the filament is correct.

T.

11/25/2010 1:10:46 AMPeter G Balazsy
I guess Thom ... that would depend on the filament arrangement.... right?
If it's series and a 150ma tube string is expected .. but a 300ma tube is used in that string... that filament may not get hot enough at all to even work..
So radio may not work... if at all.
Right?

11/25/2010 8:22:20 AMThomas Dermody
True. I also explained that earlier, too. It appears here, considering that all of the tubes mentioned are 6.3 volt tubes, except for the rectifier, that the tube filaments are wired in parallel, and so heater current will affect gain little, if at all (mostly power output tubes are affected by cathode size and necessary heater current to heat said cathode). What is affecting performance is the switch from a remote cut-off tube to a sharp cut-off tube. Sharp cut-off tubes have much more gain than remote cut-off tubes. For most audio work only sharp cut-off type tubes should be used. Remote cut-off tubes may be used in audio work, but are unnecessary, and are better suited for RF work where variable bias will be employed to vary gain.

An example of how filament current has little to do with gain is the comparison of the 6J7 and the 6W7 type tubes. The former has .3 ampere filament and the latter has a .15 ampere filament. Both have similar gain, and it will most likely be noted that both amplify equally (as I have noted, since I own both types of tubes). Only in cases of high power would the cathode size (and, indirectly, filament current draw) be of concern. Both tubes will, of course, function similarly in a parallel filament configuration. On the other hand, trouble will arise if a series filament string is employed, and one tube is substituted for a circuit designed for the other. The details of what will happen here can be found in the information I originally wrote further up this thread.

T.

11/26/2010 11:03:04 PMNorm Leal
Chris

The 6SS7 is a remote cutoff tube with 150 ma filament. 6SJ7 is sharp cutoff with 300 ma filament.

In a power transformer operated radio filament current makes little difference as long as it doesn't overheat.

A 6SJ7 may distort on strong stations if used in an IF stage. 6SK7 (remote cutoff) is a better sub for 6SS7 in a power transformer operted radio.

In an AC/DC radio 12SK7 will replace 6SS7. Even though voltage is different current is more important here.

Norm

:Hello all. Can a 6SS7 be used as a substitute for a 6SJ7 or could this be hazardous??Thanks for info
:



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