Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: delux1959 on March 18, 2018, 02:43:45 pm

Title: bogen chb10
Post by: delux1959 on March 18, 2018, 02:43:45 pm: I seem to have to many bogens on my hands. This one has a 7868 output tube. Id like to change it to an el84. Is it really as simple as swapping pins 9 and 7?
Title: Re: bogen chb10
Post by: kagliostro on March 18, 2018, 02:59:56 pm: You must consider some other things like B+, the OT impedance and the fact that EL84 (6Bq5) has a lower output power respect 7868

Franco
Title: Re: bogen chb10
Post by: sluckey on March 18, 2018, 03:20:30 pm: Quote from: delux1959 on March 18, 2018, 02:43:45 pm
I seem to have to many bogens on my hands. This one has a 7868 output tube. Id like to change it to an el84. Is it really as simple as swapping pins 9 and 7?
No. The sockets are not the same. And you must also consider the electrical characteristics that Franco mentioned.
Title: Re: bogen chb10
Post by: delux1959 on March 18, 2018, 06:11:40 pm: I have a noval on hand I could swap. I looked into the pate voltages on the 7868 and messured 430 vdc with no tube in the socket. Im guessing that is to much for an el84. I was looking at a tube data site and it says max voltage for Va is 300 with a 500vdc peak.
Title: Re: bogen chb10
Post by: shooter on March 18, 2018, 06:28:12 pm: Quote
with no tube in the socket.
put tube in, does it get close to schematic Sluckey posted, that's your "starting" point, my2c, restore it, sell it and buy parts for a 84 build :dontknow:
Title: Re: bogen chb10
Post by: kagliostro on March 18, 2018, 06:31:35 pm: With that B+ you can use a 6P14P-EV

http://www.tubes.ru/techinfo/HiFiAudio/6p14p.html (http://)

but if you can't use an EL84 why change the tube and don't go on with 7868 ?

Oh, I see, 7868 isn't so cheap ...

http://www.thetubestore.com/Tubes/7868-Tube-Types/Electro-Harmonix-7868 (http://www.thetubestore.com/Tubes/7868-Tube-Types/Electro-Harmonix-7868)

http://www.thetubestore.com/Tubes/7868-Tube-Types/7868 (http://www.thetubestore.com/Tubes/7868-Tube-Types/7868)

Well, go with 6P14P-EV

https://www.ebay.it/itm/2pcs-6P14P-EV-Matched-Pair-Gold-Grid-tube-EL84-6BQ5-Strong/142609594225?hash=item213431b771:g:Yh4AAOSwsFpaIXSk (https://www.ebay.it/itm/2pcs-6P14P-EV-Matched-Pair-Gold-Grid-tube-EL84-6BQ5-Strong/142609594225?hash=item213431b771:g:Yh4AAOSwsFpaIXSk)

https://www.ebay.it/itm/NOS-1pcs-6P14P-EV-Gold-Grid-tubes-7189-6B5Q-EL84-5881-6P14P-6-14/142429283470?hash=item212972648e:g:tqAAAOSwgeVZ1SBV (https://www.ebay.it/itm/NOS-1pcs-6P14P-EV-Gold-Grid-tubes-7189-6B5Q-EL84-5881-6P14P-6-14/142429283470?hash=item212972648e:g:tqAAAOSwgeVZ1SBV)

Franco
Title: Re: bogen chb10
Post by: delux1959 on March 18, 2018, 06:43:29 pm: just got a 7868 on flee bay for $30 including shipping.
Title: Re: bogen chb10
Post by: DummyLoad on March 18, 2018, 06:45:34 pm: 7868 is funky base 7591 - replace socket with octal socket and rewire for 7591 base. electro-harmonix 7591 is 22 bux.

--pete
Title: Re: bogen chb10
Post by: sluckey on March 18, 2018, 07:16:13 pm: What he said!
Title: Re: bogen chb10
Post by: delux1959 on March 18, 2018, 09:22:53 pm: i guess i need to keep looking for a schematic. My amp has an ez80 recto. at least to see what the voltages should be. I thought it was the chb10a.
Title: Re: bogen chb10
Post by: DummyLoad on March 19, 2018, 12:00:21 pm: Quote from: delux1959 on March 18, 2018, 09:22:53 pm
i guess i need to keep looking for a schematic. My amp has an ez80 recto. at least to see what the voltages should be. I thought it was the chb10a.

post a few pics?

--pete
Title: Re: bogen chb10
Post by: sluckey on March 19, 2018, 12:31:27 pm: Quote from: delux1959 on March 18, 2018, 09:22:53 pm
i guess i need to keep looking for a schematic. My amp has an ez80 recto. at least to see what the voltages should be. I thought it was the chb10a.
The chb 10 has an ez80 rectifier. The chb 10A is a later version of that same amp. It has the ss voltage doubler rectifier. Other than that change, I bet the amp circuit is very near identical. Do you really need a schematic for this simple amp?