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Old 17th July 2007, 05:07 PM   #11
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Be careful with assembly and how the wiring is laid out. I tried to build the 6AS7 OTL from glass audio years ago and all it did was motorboat extremely slow and make tubes go pop

But then again my wiring was very sloppy and I did not understand what all was involved.
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Old 17th July 2007, 05:19 PM   #12
SY is offline SY  United States
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Does the 6C33 have the same sort of plate as the 6528 or 6336? For those sorts of tubes, full warmup before applying plate voltage is very critical because the plate actually has getter material as a coating.
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Old 17th July 2007, 05:55 PM   #13
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Default Re: Use the chinese 6N13P instead of 6080

One thing I should specify is that I'm not very good at using tubes. The only reason I'm building an OTL amp is that there is no way I can afford decent components to build anything else. If someone could provide a schematic capable of working with a 200-ohm input impeadance, that would be most dandy.

I personally like the simplicity of this one:
http://webpages.charter.net/dawill/t...terman_OTL.gif

However, I'm not sure if I can reduce the number of output tubes and/or increase the voltage. This was (I think) designed for an 8-ohm load, and I'm working with a load at least eight times that.

Also, I'm not sure if it will work with the 6N13P.

Here's
Quote:
Originally posted by SY
Spaz, isolation transformers will work perfectly. I'd avoid tube rectifiers- OTLs are very demanding of low source impedance from the power supply.
Wacky source impeadance is one of the more noted sources of "Guitar sound." That said, I'll try adding a tube rectifier after the amp already works on a silicon rectifier.

Quote:
Originally posted by LineArrayNut
these are copies of russian 6H13C themselves copies of 6AS7G, but anyway in my totempole amps they are MUCH more rugged, sound better and are well behaved. $6 USD each @ diy hifi supply
More durable AND cheaper? Bada-Bing!
At $6 a tube, I can afford to use multiple pairs in the output stage. 50W into 64 or 128 ohms is the target for this amp, which from what I've read, is a much more OTL-friendly load than 8 ohms.

Quote:
Originally posted by SY
Does the 6C33 have the same sort of plate as the 6528 or 6336? For those sorts of tubes, full warmup before applying plate voltage is very critical because the plate actually has getter material as a coating.
The power switch on my amp will actually be connected to the 12v transformer. Once the amp is powered on, a simple capacitor-based timer will then turn on a relay connected to the power transformer. Hence, no risk of arcing - the tubes will get a good thirty seconds of warm-up time before any voltage is applied.
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Old 17th July 2007, 06:02 PM   #14
Jeb-D. is offline Jeb-D.  United States
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Quote:
Does the 6C33 have the same sort of plate as the 6528 or 6336?
It's my understanding the 6336 is electrically the same as 6C33C. Just the 6C33C has a bunch of added bracing to tolarate abuse, vibration, ect.
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Old 17th July 2007, 06:31 PM   #15
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Hi.

I have been meaning to build an OTL amp for some time and this thread has prompted me to search the scrap box.

Result....

16 x 6336A

Transformer 220/110 @ 5A plus 12v @ 10A

10000uF / 400v x2


Should be good for a start?


Andy
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Old 17th July 2007, 06:53 PM   #16
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Well, I'm not the first to do this, as it turns out.
http://www.renditionaudio.com/evolution.html

I'm going to use a simpler preamp, though. I have yet to meet a musician who would rather have his controls on his amp (pain in the *** to get to mid-song) than attached to a handy-dandy pedal.

However, there's a rather nifty doohickey that they overlooked: 32 ohm drivers - Jensen's MOD10-50-32. Their MOD series has a reputation for high "bang for the buck", and at 32 ohms, two in series gives me a very OTL-friendly 64 ohm load. And if the guitar amp works well, I might turn it into a 4-driver cabinet - 128 ohms!
http://www.andrewsamplab.com/mods_series.htm
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Old 18th July 2007, 03:35 AM   #17
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Surely you could afford transformers from Edcor?

http://www.edcorusa.com/products/class_x.html

Their "high end" models still cost <$50 each. The closest to that is Hammond which is near $100.
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Old 18th July 2007, 03:53 AM   #18
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Quote:
Originally posted by astouffer
Surely you could afford transformers from Edcor?

http://www.edcorusa.com/products/class_x.html

Their "high end" models still cost <$50 each. The closest to that is Hammond which is near $100.
Well, maybe. The point of this is to build a really, really, really cheap guitar amplifier capable of producing 30 watts or more.

I already have a bunch of caps and resistors, the transformers (120v->240v step-up units, or a pair of isolation transformers) are dirt cheap, and the tubes are $7 each.
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Old 18th July 2007, 06:45 AM   #19
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Quote:
It's my understanding the 6336 is electrically the same as 6C33C
No, that is not really correct, they are quite different which you can see if you compare the specs like here http://www.tubetvr.com/favtube.html they are similar but that you can say about almost all regulator triodes.

My experience of 6336 is very bad, they are not built very well and can't withstand almost any over current for any time however short, one reason why I gave up on OTL's for a long time was due to this experience, (and the price of 6336)

For long life and good performance it is important to burn in 6C33C in the correct way and it is mandatory to switch on heater at least 30 seconds before the anode voltage. With correct burn in the specs of these tubes are very similar, I bought a bunch of 100 from GS tubes in Russia and at the same grid voltage and at 200V anode voltage I didn't get bigger variation of anode current than +- 10%, I think that is quite good. Viktor Khomenko at BAT have reported that they get a failure rate of new unused tubes of about 1% which is not to bad either.

If using 6C33C in parallel it is important to derate current, (there are values for this in the data sheet) and use cathode resistors for each tube, it is a major difference to build an OTL with just 2 tubes or to use multiple parallell ones, the difficulties mutiplies even faster.

Regards Hans
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Old 18th July 2007, 03:43 PM   #20
Jeb-D. is offline Jeb-D.  United States
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Quote:
No, that is not really correct, they are quite different
Ah, yes they are quite different. I had been misinformed.


Why did you buy 100 6c33c's? Are you affraid they will become unavailable?
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