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6P41s vs 7868
6P41s vs 7868
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Old 8th February 2018, 06:17 AM   #1
huggygood is offline huggygood  France
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Default 6P41s vs 7868

hello everyone
I have an unknown original amp(no schematic) with a double push of 7868.
these lamps are at the end of life and I have in stock 2x4 6p41s.
I would like to know if any of you have already made swap 7868 / 6p41s and if he can give me some ideas for implementation and modification.
thank you
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Old 8th February 2018, 10:58 AM   #2
Tesla88 is offline Tesla88  Italy
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Intrested since i have an old Rowe R-4359A without 7868's while i have some 6p41s on the shelves
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Old 8th February 2018, 11:45 AM   #3
davorin is offline davorin  Croatia
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You need much more negative voltage for g1 (need ~cca -65V for 6P41S bias) than the amplifier can give it. Perhaps you could use the high voltage winding of course with the modifications, and certainly with the change in the value of the adjustment elements for bias.
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Old 8th February 2018, 12:44 PM   #4
toprepairman is offline toprepairman  United Kingdom
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This is an interesting thread.
I just recently picked up a Rowe (juke box) amp with very knackered 7868's.
Ok so simple solution is to get a set of 6P14's. When they arrived I put them on the curve tracer and couldn't quite believe the phenomenal performance, thinking this will need much more bias than the standard 14 Volts. Being a bit busy I put it to one side but made a mental note that probably a conversion to auto bias is most likely the optimum solution.
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Old 8th February 2018, 01:01 PM   #5
Eli Duttman is offline Eli Duttman  United States
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New Sensor currently manufactures 7868s.

What does Rowe's bias supply circuitry look like? If it's a simple tap on the rectifier winding that's 1/2 wave rectified, install a 1/2 wave voltage doubler.
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Last edited by Eli Duttman; 8th February 2018 at 01:02 PM. Reason: spelling/omitted word
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Old 8th February 2018, 04:11 PM   #6
huggygood is offline huggygood  France
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i'm very happy with your Rowe amplifier but mine is not a Rowe !
after investigation,mine is the same to Hitone H300 but with no phono,no grave/aigue correction,no balance etc etc etc ...
the shematic
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Old 8th February 2018, 06:10 PM   #7
artosalo is offline artosalo  Finland
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6P41S is a high current tube.
It has about the same anode with 170 V screen voltage than 7868 has with 400 V (Ug1 = 0 V).

As a PP-UL amplifier, 6P41S works best with some 300 V supply voltage and 4k load impedance. Some 20...25 W is available.
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Old 8th February 2018, 09:25 PM   #8
Wavebourn is offline Wavebourn  United States
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6P41s vs 7868
Already discussed.
6P41S is totally different tube, even though looks kind of similar. Since your amp can provide higher swing, you can try 6L6 tubes. In such case it may work, with less feedback as the result.

7868 tubes - replace with 6L6's?
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Old 9th February 2018, 05:42 AM   #9
huggygood is offline huggygood  France
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ok thank's
I will opt for a quad of 7591 and change the sockets.
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Old 9th February 2018, 05:54 AM   #10
davorin is offline davorin  Croatia
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Quote:
Originally Posted by huggygood View Post
ok thank's
I will opt for a quad of 7591 and change the sockets.
Why?
7868 – 1 Quartett selektierte Electro-Harmonix Rohren-Tubes matched quad (~7591) | eBay
Brand New Electro-Harmonix 7868 Plate Current Matched Quad (4) Vacuum Tubes | eBay
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