You may laugh..but don't waste your time trying to dissuade me. 300B preamp.

Bas Horneman · 19th May 2005, 08:59 AM

I want to build a preamp with a 300B. Why?

Simple..I want to build a preamp with a DHT tube and don't want to buy another tube for a while. (Cash and too many unused tubes in cupboard already)...at first I was thinking...gonna build a nice choke loaded TJ 205d preamp or 101d...But that's a lot of bucks to fork out...then I thought...but I already have some DHT's "in stock" for years that I have not used (that is where the 300B's come into the picture). Plus I have a Hybrid Gary Pimm CCS built for 60mA (Just need some EL34's..but they are cheap)

I may or may not use a 7n7 SRPP stage or so before...to get some gain first.

Any suggestions...should I parafeed because I have a CCS already?

Manley Labs have done a 300B preamp and so have a company in Singapore (any idea about the topologies of these companies?)
Pete Millet also has a low mu preamp where he uses say a 6AS7 with EL34 current source...I might do something like this as well...substituting the 300B in place of the tubes Pete has suggested. (Anybody built this baby?) http://www.pmillett.com/lowmu_preamp.htm

I have this idea that there are more folks that have built a 300B preamp but are afraid of the Environmental lobby groups...and won't admit to it?

Experiences and suggestions are very welcome.

slowmotion · 19th May 2005, 09:22 AM

Hi Bas, all

I used a 300b linestage for a while,
it sounded very "organic" , dynamic and musical,
but I wouldn't really call it "accurate", whatever that means

I used the 300b chokeloaded, with a cap on the output.
Regulated DC filaments.

cheers

Bas Horneman · 19th May 2005, 09:26 AM

Quote:

it sounded very "organic" , dynamic and musical,

Thanks slowmotion!!...I am looking for organic, dynamic and musical... :-)

What value choke did you use? Do you remember what cathode resistor / operating point you used?

Who forced you to say it sounded accurate? GreenPeace?

I also have a DC reg in my cupboard..just waiting to be applied.

Regards,
Bas

slowmotion · 19th May 2005, 09:59 AM

It's been a while,
but if I remember correctly
( fat chance

)
probably 300V and 60-80 mA
or something like that.
It's nice to put a bit of current through it.
Regulated DC on the filament with catode return taken from the negative side of the filament only.
Choke was a Tamura output transformer with the secondarys left floating, output cap was a Mundorf I think.

hope this helps

cheers

Bas Horneman · 19th May 2005, 10:04 AM

Thanks Jan!

Quote:

Regulated DC on the filament with catode return taken from the negative side of the filament only

Good tip...thanks again. (never used a DHT before )

planet10 · 19th May 2005, 10:09 AM

... go for it...

look foward to another of your sculptures in wood...

dave

Bas Horneman · 19th May 2005, 10:18 AM

Quote:

... go for it...

Thanks!

Did you ever see my darling (still not completed)

Eli Duttman · 19th May 2005, 10:55 AM

Bas,

Use current regulated DC on the 300Bs' filaments. There are NUMEROUS remarks around about "washed out" sonics when voltage regulated DC is used with DHTs.

FWIW, I would float the filament supply and rig a 4PDT switch to periodically reverse the DC polarity applied to the filaments. The 300B was designed to be heated with AC. The potential gradient associated with DC heating can shorten service life. Flip/flopping the DC polarity about once a month (more often, if you like) will compensate for the problem.

Consider using unbypassed cathode resistors. The 300Bs will be linearized without significantly altering their overall character.

Bas Horneman · 19th May 2005, 11:23 AM

Hi Eli,

Will do...

I've got a voltage reg followed by a current reg...so I might take out the voltage reg part.

The thing I don't really understand about a current reg is this :
With what voltage do you need to supply it? AFAI understand it ...it does not really matter..since the filament will only be supplied with 1,2A? So I can supply 8V or 12V does not matter?

I usually leave out the cathode resistors. But this time round I want to also add a switch so that I can hear myself the advantages/disadvantages.

Thanks and regards,
Bas

SY · 19th May 2005, 11:55 AM

Well, I had suggested a phono preamp using a 6528 some time back, so a 300B linestage is only the second most ridiculous idea I've heard of.

You might think about incorporating that into this preamp. If you're going to make your electricity provider rich, may as well go all the way.

19th May 2005, 08:59 AM	#1
Bas Horneman diyAudio Moderator Emeritus Join Date: Apr 2002 Location: The Netherlands Blog Entries: 18	You may laugh..but don't waste your time trying to dissuade me. 300B preamp. I want to build a preamp with a 300B. Why? Simple..I want to build a preamp with a DHT tube and don't want to buy another tube for a while. (Cash and too many unused tubes in cupboard already)...at first I was thinking...gonna build a nice choke loaded TJ 205d preamp or 101d...But that's a lot of bucks to fork out...then I thought...but I already have some DHT's "in stock" for years that I have not used (that is where the 300B's come into the picture). Plus I have a Hybrid Gary Pimm CCS built for 60mA (Just need some EL34's..but they are cheap) I may or may not use a 7n7 SRPP stage or so before...to get some gain first. Any suggestions...should I parafeed because I have a CCS already? Manley Labs have done a 300B preamp and so have a company in Singapore (any idea about the topologies of these companies?) Pete Millet also has a low mu preamp where he uses say a 6AS7 with EL34 current source...I might do something like this as well...substituting the 300B in place of the tubes Pete has suggested. (Anybody built this baby?) http://www.pmillett.com/lowmu_preamp.htm I have this idea that there are more folks that have built a 300B preamp but are afraid of the Environmental lobby groups...and won't admit to it? Experiences and suggestions are very welcome. __________________ Boatanchor amps forum My "adventures" in audio

19th May 2005, 10:09 AM	#6
planet10 frugal-phile(tm) diyAudio Moderator Join Date: Oct 2001 Location: Victoria, BC, NA, Sol III Blog Entries: 4	... go for it... look foward to another of your sculptures in wood... dave __________________ community sites t-linespeakers.org, frugal-horn.com ........ commercial site planet10-HiFi p10-hifi forum here at diyA

19th May 2005, 10:55 AM	#8
Eli Duttman diyAudio Member Join Date: Apr 2004 Location: Plainsboro, NJ	Bas, Use current regulated DC on the 300Bs' filaments. There are NUMEROUS remarks around about "washed out" sonics when voltage regulated DC is used with DHTs. FWIW, I would float the filament supply and rig a 4PDT switch to periodically reverse the DC polarity applied to the filaments. The 300B was designed to be heated with AC. The potential gradient associated with DC heating can shorten service life. Flip/flopping the DC polarity about once a month (more often, if you like) will compensate for the problem. Consider using unbypassed cathode resistors. The 300Bs will be linearized without significantly altering their overall character. __________________ Eli D.

19th May 2005, 11:23 AM	#9
Bas Horneman diyAudio Moderator Emeritus Join Date: Apr 2002 Location: The Netherlands Blog Entries: 18	Hi Eli, Will do... I've got a voltage reg followed by a current reg...so I might take out the voltage reg part. The thing I don't really understand about a current reg is this : With what voltage do you need to supply it? AFAI understand it ...it does not really matter..since the filament will only be supplied with 1,2A? So I can supply 8V or 12V does not matter? I usually leave out the cathode resistors. But this time round I want to also add a switch so that I can hear myself the advantages/disadvantages. Thanks and regards, Bas __________________ Boatanchor amps forum My "adventures" in audio

19th May 2005, 11:55 AM	#10
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	Well, I had suggested a phono preamp using a 6528 some time back, so a 300B linestage is only the second most ridiculous idea I've heard of. You might think about incorporating that into this preamp. If you're going to make your electricity provider rich, may as well go all the way. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

19th May 2005, 09:22 AM	#2
slowmotion diyAudio Member Join Date: Nov 2002 Location: Norge	Hi Bas, all I used a 300b linestage for a while, it sounded very "organic" , dynamic and musical, but I wouldn't really call it "accurate", whatever that means I used the 300b chokeloaded, with a cap on the output. Regulated DC filaments. cheers

19th May 2005, 09:59 AM	#4
slowmotion diyAudio Member Join Date: Nov 2002 Location: Norge	It's been a while, but if I remember correctly ( fat chance ) probably 300V and 60-80 mA or something like that. It's nice to put a bit of current through it. Regulated DC on the filament with catode return taken from the negative side of the filament only. Choke was a Tamura output transformer with the secondarys left floating, output cap was a Mundorf I think. hope this helps cheers

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