SE 300B Integrated Amp: Help choose circuit design

[xenithon]

Hi All,

I am having a 300B SE integrated amp built, and the builder an myself were originally planning on using an Aikido circuit. I came across much reservation though due to the limite gain (as the Aikido was designed as a preamp) so we have explored other options. We discussed these in length this morning and have narrowed the choices down to the list below. I'd appreciate any feedback or recommendations on which to opt for.

1. 12AV7/12BH7A
- 12AV7 input tube, wired in parallel
- 12BH7A driver tube (not 100% certain how to wire this; could parallel both to yield a little extra gain, but at what cost?)

2. 12AV7/EL34
- 12AV7 input tube, wired either in parallel, as a mu follower, or SRPP
- EL34 driver tube, wired as a triode strapped pentode

3. Pentode Aikido (http://www.diyaudio.com/forums/showthread.php?s=&threadid=65708)
- we are not sure which tubes would be used here
- would a pentode (e.g., EL84) be used as input and a triode (12BH7A/ECC99) as driver tube?
- or visa versa: triode as input, pentode as driver (like option 2 but Aikido)?

If possible, please try limit suggestions/comments to the above three (to keep my indecisive nature in check)

With regards,
X

PS. I did have a thread earlier regarding OPT choice, but that decision has been taken so thought it better to start a new thread for this.

 

[xenithon]

Sorry, I almost forgot the one other option (amp builder just reminded me of it):

4. 12AV7/12BH7A (based on this design)
- 12AV7 as voltage amplifier
- 12BH7A in SRPP as driver

Cheers,
X

 

[xenithon]

Hi all,

Following some more discussion with various people, I have narrowed it down the following combinations

1. 12AV7/12BH7/300B
- both 12AV7 and 12BH7 would be wired in parallel
- I could also at some stage experiment with SRPP
Question: which one should be wired in SRPP - the 12AV7 input tube or the 12BH7 driver?
2. 12AV7/EL34/300B
- the EL34 would be wired as a triode strapped pentode
- I have seen this implemented in various ways such as here (which seems to use the full 12AT7) and here (which seems to only use 1/2 the 12AT7)
Questions:
- which of the above schematics would be better?
- can I use the 12AV7 in place of the 12AU7?
- would I require a CCS or can this be implemented without one?

Cheers,
X

 

[mhconley]

X -

Have you received any input on this thread? Have you built either of the two amps in option 2? I am considering building the first using the full 12AT7 and am looking for feedback on the schematic you linked...

Thanks,

Martin

 

[Tetrode]

Try a 2 stage amp with just the EL84 driving the 300B.

 

[nicoch58]

there are tre nice design of thorsten , two stage with pendode , lady D+
417a
310a we can use the svetlana copy
G3m

I think I will try g3m or 310a

 

[alexg]

Try a 2 stage amp with just the EL84 driving the 300B.

Anybody done this?

 

[Bas Horneman]

Try a 2 stage amp with just the EL84 driving the 300B.

I have. I liked it. (EL84 in pentode). But you might not. That is the problem. It is best to build a few well known/well received 300B amps and listen to them in your system.

A little something about Herb Reichert's "Flesh and Blood":

Apparently if you want to build the "Flesh and Blood" you must build it exactly as specified. Not my own experience but something I got told by someone who has tinkered with a lot of 300B designs.

 

[Bas Horneman]

3. Pentode Aikido (pentode aikido driver for 300b)

I never tried that one. But since I used the 6N6P I've become curious. But I have many other things higher on the priority list at the moment.

 

[rock4016]

Hi All,

I am having a 300B SE integrated amp built, and the builder an myself were originally planning on using an Aikido circuit. I came across much reservation though due to the limite gain (as the Aikido was designed as a preamp) so we have explored other options. We discussed these in length this morning and have narrowed the choices down to the list below. I'd appreciate any feedback or recommendations on which to opt for.

The Aikido does have enough gain to drive the 300B. Options would include 6SL7/6SN7 or 12AX7/6CG7 and some others.

 

[JimW]

EL84 Drivng 300B

I have done this, (and use at present this configuration). Wire the socket to accommodate sv-83/6n15p-eb and you can use either tube. I prefer the 6np15-eb to the EL84. T.Loesch had a description of this amp on his old website, as well as in the archives of DIY. I used a cap bypassed voltage divider to supply the screens (around 135v) and have about 260 on the plate through a 12k resistor. Plate current is around 10-12 ma, so the tube should last forever. Power supply needs to be pretty smooth, as this driver doesn't offer much in the way of ripple rejection.

 

[Raj1]

I recently changed my 300B monoblocks from choke loaded 6N1P to a grid biased (coin cell) triode wired D3A after a conversation with Thorsten. It's a massive improvement over the 6N1P when it comes to dynamics, imaging and minute details. A very complete 2 stage amplifier that will work with most sources without needing an active preamplifier in most configurations. I'll take this opportunity to say thanks to the man for putting up with my questions.

-Raja

 

[Bas Horneman]

Was the d3a choke loaded? Do you have a schematic?

 

[Raj1]

Hi Bas,

Yes choke loaded using an Electraprint plate choke. I don't have a schematic unfortunately.

Operating point Thorsten recommended was around 180V on the anode with a 2V coin cell in series with the grid and grounded cathode. Could not find a 2V coin cell so we went for 170V on the anode with a 1.5V (1.58V) silver oxide coin cell.

Hope this helps..
Raja

 

[Bas Horneman]

Hope this helps..

It does thanks Raja.

 

[Raj1]

If you do try it and manage to source some 2V coin cells let me know please Bas. I tried cathode LED bias but prefer the sound of the grid battery method. Only other tube I'd like to try out is a C3M, though I believe the are supposed to sound better pentode wired which means losing the plate choke. I've pinged TL and asked him for some operating parameters and will post here if he recommends anything.

 

[JPeitzman]

I haven't tried this, but with the talk of EL84's as drivers this might be of interest if you haven't seen it already. Has to be adjusted on a per-tube basis (screen voltage), so no simple tube rolling. However, good PSRR for a pentode stage, low output impedance, and low distortion (even at 90+ volts out) just to name a few.

Link to the full page:
http://www.pimmlabs.com/web/drivers.htm

 

[alexg]

Thanks guys.

I will breadboard an el84 (pentode) driven 2a3 for now (I don't have the 300B yet).

Am planning to regulate the el84 screen using 0D3 regulator.

 

[alexg]

I have. I liked it. (EL84 in pentode). But you might not. That is the problem. It is best to build a few well known/well received 300B amps and listen to them in your system.

A little something about Herb Reichert's "Flesh and Blood":

Apparently if you want to build the "Flesh and Blood" you must build it exactly as specified. Not my own experience but something I got told by someone who has tinkered with a lot of 300B designs.

Hi Bas,

How is the EL84 driven 300B different from a 6sn7 driven 300B? (I just want to get a general idea of how it will sound.)

Thanks.