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 Post subject: WTB pair of 6BQ5 tubes, possibly 4
PostPosted: Feb Mon 12, 2018 3:24 pm 
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Joined: Nov Wed 01, 2017 4:36 pm
Posts: 105
Location: Lafayette, NJ 07848
I have one bad 6BQ5 (EL84) tube in a Magnavox amplifier and am thinking it may be best to replace one pair to keep reasonably matched. The other three are Magnavox branded. I guess a matched quad would be best, but 2 is fine. I'd like to have some backups on hand too.

Thanks,
Rich


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 Post subject: Re: WTB pair of 6BQ5 tubes, possibly 4
PostPosted: Feb Mon 12, 2018 7:42 pm 
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Joined: Sep Tue 15, 2015 1:16 am
Posts: 164
Location: 18424 PA
https://ubuyguitars.com/product/el84-po ... r-chinese/


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 Post subject: Re: WTB pair of 6BQ5 tubes, possibly 4
PostPosted: Feb Mon 12, 2018 9:46 pm 
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Joined: Dec Tue 09, 2008 2:49 am
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Location: Farmington , Michigan
I have NOS and used. Let me know what you're looking for.
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 Post subject: Re: WTB pair of 6BQ5 tubes, possibly 4 (EL84)
PostPosted: Feb Wed 14, 2018 8:09 pm 
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Joined: Nov Wed 01, 2017 4:36 pm
Posts: 105
Location: Lafayette, NJ 07848
Update: Turns out the existing tubes I have are Sylvania black plate. Anyone have two of these used? One is failing fast and starting to red plate now.

I am still open to considering other tubes in pairs and quads. Tell me what you've got and if possible please send a picture. I didn't realize how expensive these tubes can be but I am learning that some people take their 6BQ5's very seriously ;)

I am reading up on the various brands and such and would prefer to avoid the Russian versions for now. So far I like Sylvania, GE, Siemens, and Mullard.


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 Post subject: Re: WTB pair of 6BQ5 tubes, possibly 4
PostPosted: Feb Wed 14, 2018 11:31 pm 
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Joined: Sep Tue 15, 2015 1:16 am
Posts: 164
Location: 18424 PA
You may have circuit problems if it's red plating, does if follow the tube if you swap sockets?


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 Post subject: Re: WTB pair of 6BQ5 tubes, possibly 4
PostPosted: Feb Thu 15, 2018 1:36 am 
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Joined: Dec Tue 01, 2015 5:31 am
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Location: Columbus Ohio
not sure if you like "imported" tubes, $32 for matched quad set
https://www.ebay.com/itm/NEW-Sovtek-EL8 ... 3068!US!-1

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 Post subject: Re: WTB pair of 6BQ5 tubes, possibly 4
PostPosted: Feb Thu 15, 2018 2:11 am 
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Joined: Nov Wed 01, 2017 4:36 pm
Posts: 105
Location: Lafayette, NJ 07848
n3uvt wrote:
You may have circuit problems if it's red plating, does if follow the tube if you swap sockets?


Yes. Follows tube in any socket.

This is a common cathode bias circuit (one resistor for all 4 tubes). Two idle at 6-7ma and two at 20 and 42ma. The red just started so maybe current has gone up in the latter. Will measure again tonight. This tube also is developing positive grid voltage (+2 to +3 volts now). There are no leaky capacitors. This voltage is developed due to outbound current through grid resistor alone. Probably cathode material migration to grid I'm told. Tubes all test good. This "bad" one is the best or all at 103% ;)

I may separate the bias into two just to see what happens. This one tube is dominating the show and causing cathode voltage of 14.8 for all.

Still sounds great:)

Here is what they look like:

Image


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 Post subject: Re: WTB pair of 6BQ5 tubes, possibly 4
PostPosted: Feb Thu 15, 2018 2:31 am 
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Please use the PM system for any other discussion.
Thanks.
Phil

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 Post subject: Re: WTB pair of 6BQ5 tubes, possibly 4
PostPosted: Feb Thu 15, 2018 6:46 pm 
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Joined: Apr Sat 04, 2015 6:15 am
Posts: 750
Location: Dos Rios, CA.
Photo of Sylvania tubes.


Attachments:
(4) 6BQ5 Sylvania 2.JPG
(4) 6BQ5 Sylvania 2.JPG [ 104.66 KiB | Viewed 236 times ]
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