• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

The end of the 300b Dream?

Hi
After having been set (pardon the pun) on building 300b monoblocs and buying the iron, I am left wondering wether i should go ahead given the dramas with valve life and quality.
I have a chinese version and bluntly speaking whould love 15 watts or so so I had thought of a parallel version.
Single tube alternatives?
845.. scary volts inside and am not willing to risk it.
6c33c Maybee provided I could get some reliable ones and good sockets and 8 amp heater supplys....
kr tubes.. expensive, dont sound like a 300b and future supplys questionable...
So have i missed anything? What have others done for 15 watts and above of set pleasure?
regards
Nick
 
duderduderini said:
Hi
After having been set (pardon the pun) on building 300b monoblocs and buying the iron, I am left wondering wether i should go ahead given the dramas with valve life and quality.
I have a chinese version and bluntly speaking whould love 15 watts or so so I had thought of a parallel version.
Single tube alternatives?
845.. scary volts inside and am not willing to risk it.
6c33c Maybee provided I could get some reliable ones and good sockets and 8 amp heater supplys....
kr tubes.. expensive, dont sound like a 300b and future supplys questionable...
So have i missed anything? What have others done for 15 watts and above of set pleasure?
regards
Nick

well - if you have doubts ......... maybe you aren't nutz enough?

;)
in that case - go for any of craziest Pass amps .......

or - find less demanding spks, and use some less expensive tubes for output ones ............ buy enough of them for rest of life
 
I was in the same dilemma as you- 6C33C-B vs. 300B x 2 to drive a commercial speaker (LSA1) that I really like.

I have embarked on a project to build a pair of PP 300B. Then I heard a LAMM driving them, so I thought of building the 6C33C-B circuit of Borberly Audio, but then I can't get the tubes, so I'm back with the PP 300B....

I'm nuts, maybe I should build them both. :xeye:
 
duderduderini said:
Hi
After having been set (pardon the pun) on building 300b monoblocs and buying the iron, I am left wondering wether i should go ahead given the dramas with valve life and quality.

You've come this far, go for it. Quality may have been an issue in the past, but it's been improving lately.

Single tube alternatives?

Unforch, there really aren't any. The original 300B came out the same year that the 807 did. That was the end of the triode era, and there is a definite lack of AF power triodes (though RF triodes were rather common, but as "zero bias" tubes for the most part: Class A2 required, and the usual pentode problems: high rp's, higher h3 and above) in the same class as the 300B.

What have others done for 15 watts and above of set pleasure?
regards
Nick

What I'm doing is working on a design for an 845 based SET. The big volts don't bother me, the OPT iron is available (from Lundahl, not cheap, but it's available) and PSs can be made easily from "control xfmrs". Other than that, perhaps trioded 813s (still big volts required) or perhaps some big HD pents can be trioded.

I was originally considering a SET based on the 812: moderate voltages, Class A2, decent output. However, Jack at Electraprint couldn't promise that the necessary 8K4 : 8R OPT wouldn't be good enough for anything other than a gee-tah amp. (Kudos to Jack for being honest about this, and not ripping me off :cool: :) ) SET gee-tah amps aren't of any use to me, and not exactly a practical proposition for a player. So I dropped that design if favour of the 845.
 
If you already bought the iron for 300b you should stick it out.

For future SE builds, I would recommend the 6c33c. I've gotten 15Wrms out of one. The 6c33c horror stories come from people using them in designs that have multiples in parallel and/or in circuits that require precise balance.

Cathode bias SE - you can just pop one in and from time to time clean the pins and sockets. That's it!

Fixed bias SE - pop it in, bias it (be sure to design it so the pot doesn't have a lot of range), let it heat up for 30min then adjust the bias again. Then use the amp regularly for a few days to a week, then re-bias it. After that point you really shouldn't have to mess with it for a long time. Just every few months clean the pins and sockets and re-check the bias if you want to be carefull. I ran my fixed bias 6c33c SE for a year without problems (I didn't clean the pins, sockets or have to re-bias it). It is now parted out to donate parts to a better 6c33c design i'm building.

The 6c33c sounds excellent and has a very unique tone. It's Probably my favorite tube.
 
Re: Where does one procure a decent 6c33c?

duderduderini said:
Hi Jeb
Do you have a reliable source of these tubes?
How would you describe the sound of them.. I dont mind smooth sounding tubes with good bass at all
regards
Nick

I would be interested in a good source as well, as my local friends distributing the BAT said they got theirs expensive.

What I heard from the LAMM + Von Schweikert DB99 was astounding transparency, and palpability. Somewhat spooky really, but it has great tight bass, and high frequency extension to boot.

I was moved while listening to the CD "The Fountains of Bellagio, volume 3"
 
I got a box of 10 for $80 on ebay a couple years ago from a guy named Anthony Welsch. There was 1 that was defective, but the rest were good and unused. Now they go for around $15 US each, which is more expensive than before, but way cheaper than a 300B.

What I heard from the LAMM + Von Schweikert DB99 was astounding transparency, and palpability. Somewhat spooky really, but it has great tight bass, and high frequency extension to boot.

That nails it on the head. I didn't want to sound like a fuitcake and say that it has a haunting/eary/spooky tone to it. But, it really does. Glad I'm not the only one who thought so. It has the great midrange presence you would expect from an SE, but it has crystal clear highs. And the bass is definatly not lacking. It is tight by tube amp standards, but still slighly round in some configurations. Which I don't really consider a bad thing, it just gives it a touch of vintage tone.
 
Do you have a reliable source of these tubes?

By directly from Russia at tube.ru or at gstube.com there are no reason to go through one or more distributors that just add to the price. The GStube price is now as low as 9 USD per tube and about 20USD in P&P for a set of 4 tubes . I have bought quite large quantities of 6C33C from this source and had no problems.

In order to avoid problems with the 6C33C follow some simple rules:

Switch on heater only and let it stay for that up to 2 hours

Switch on anode voltage and let the anode current go up to ~200mA and let is stay there for 2 hours.

Re adjust bias after about 10 hours operation.

Always switch on the heater at least 1 minute before anode voltage.

Following these rules you will have reliable tubes withe very long life, I have now used the same set of tubes in my own OTL amp for about 7 years without failure or loss of performance.

Regards Hans