EQUIPMENT FORUMS >> SE84UFO25 >> Rectifier Tubes For The 25th

Message started by MrDerrick on 02/06/19 at 17:40:56

Title: Rectifier Tubes For The 25th
Post by MrDerrick on 02/06/19 at 17:40:56

I have read all the posts that I could find on rectifier tube types for the 25th. From what I gather, the first cap in the 25th is 47uf.

While I can not find the manual online for the 25th anymore, the copy that I downloaded states that a type 80 rectifier can be used and the picture of the 25th on site shows an 80 in use.

So is there a range of rectifier first cap ratings that will work?
Say 32uf (type 80) up to 47uf  (Aqua 274B) all the way up to 60 uf (GZ32) ?

While the EML 5U4G Mesh is rated at 40 uf for the first cap, can it also be considered since it falls between the 80 and the Aqua 274B?

Title: Re: Rectifier Tubes For The 25th
Post by jslateiv on 02/07/19 at 19:10:19

I was looking pretty hard at a EML 5u4G.  I def. think it can be considered and would/will be fine.  Technically (from the data sheet) 5U4GB have a max of 40uf as well and that is what the amps are built around.   In a 5U4GB datasheet it also mentions that a higher cap. is allowed provided that the initial current draw at startup or hot-switching is further regulated by plate-supply resistance,..   min. values are given for 40uf operation.   In that most all (I believe) of Steve amps seem to work well with a variety of rect. tubes including ones that specify a much lower cap.,  I think that the plate supply resistance (trans legs) are already sufficiently high enough to limit the current draw for a larger cap.  Just how much idk,...  Perhaps Steve can/could weigh in on the suitability of suitability / risk of failure/arching when using rect. with a low cap. maximum.  and or with the PT resistance on the sec. legs.

Title: Re: Rectifier Tubes For The 25th
Post by jslateiv on 02/21/19 at 15:57:43

Hey Robert,   did you ever get a different Rect. to try out?  The EML perhaps?   I ended up grabbing a Aqua 274B and can report that it is a SUPERB rect. in the 25th-A amp.  A lot of others here really like it and they are spot on!   I am still very curious about the sound of the EML though.

Title: Re: Rectifier Tubes For The 25th
Post by MrDerrick on 03/25/19 at 02:11:37

Hey John,

I missed your post, sorry about that.
I picked up an Aqua and an EML. ( and a globe 80 )
The EML is a freaking huge rectifier!
It has been quite awhile since I had to run an amp in.
I ran the 25th for the first 30 hours or so with the Aqua.
Then I switched it out for the EML. ( the older I get the less patience I have )
I know that I should just let everything settle in before tube rolling, but from the good report on the Aqua, I thought why not just start with it.
Immediately after firing up the EML though, the illusion of space increased dramatically.
I don't know if the Aqua needs more conditioning or if the EMLs are conditioned extensively at the plant, but the difference was immediately noticeable without running in the EML.
Do not expect to view the mesh plate glow head on, the key way is at 90 degrees so you view the EML mesh plate skinny side, unless your 25th is placed that you view it from the side.
I also started right off with a seasoned HP Amperex 7308 Red Tip PQ in the input socket.
I am a bit over 50 hours of run in and it is sounding very very nice.


Title: Re: Rectifier Tubes For The 25th
Post by jslateiv on 03/25/19 at 15:53:57

Awesome,   thanks for the update Robert!  Good to hear on the EML,   it is now on my tube short list,  lol.   If you have any E288cc's laying around,  toss on in for the input and see what you think.   So far it may be my fav for an input tube.  Very smooth.

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