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OvrReactor
 
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Default KT88 or KT90 for scratch built bass amp???

Anyone care to comment on which tube would be "better" for a high powered bass
amp? By "better", I mean more reliable when abused. You know how we bassists
are! I've been wanting to try my hand at building a high powered all tube bass
amp, but I figure someone else's experiences will help save me a lot of time
and money. I've built a few bass amps in the 100 to 200 Watt range, but I'd
like to take things up a few notches. And if I'm happy with the results, MAYBE
I might actually make a few for sale...

But I sure as heck couldn't call them "Mitchell Amps". People might think I'm
the "other" Tom Mitchell that made amps in Riverside, California back when I
was still in High School, and then people would expect me to FIX all those
bargain-basement Boogie clones...

By all means, POST your response, but PLEASE respond by EMAIL too! I;m only
drop in to this newsgroup two or three times a month.

Best regards,
Tom Mitchell
website - http://members.aol.com/ecc81
website - http://www.over-reactors.com
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Sam Byrams
 
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Phooey. A tube BASS amp needs to be a general purpose power amplifier,
not a guitar amplifier. Study true classics like the Altec 260B,
1570B, Mac MI200, and other audio amplifiers using real power
tubes,211s, 811s,812s, and up-look at a Varian Eimac catalog. If it
does not have at least 1200 vdc on the plates I am not interested at
all.
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Lord Valve
 
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Sam Byrams wrote:

Phooey. A tube BASS amp needs to be a general purpose power amplifier,
not a guitar amplifier. Study true classics like the Altec 260B,
1570B, Mac MI200, and other audio amplifiers using real power
tubes,211s, 811s,812s, and up-look at a Varian Eimac catalog. If it
does not have at least 1200 vdc on the plates I am not interested at
all.


Play much on the road?

I didn't think so.

LV




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TubeGarden
 
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Hi RATs!

Flinging =C= 6550 are really pretty decent for cheaper than the oh so trendy KT
posers

Tubes is great, but, all bidness is a racket

Happy Ears!
Al


Alan J. Marcy
Phoenix, AZ

PWC/mystic/Earhead
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anybody-but-bush
 
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----- Original Message -----
From: "Jon Yaeger"
Newsgroups: rec.audio.tubes
Sent: Saturday, July 03, 2004 2:29 PM
Subject: KT88 or KT90 for scratch built bass amp???


: What happens when you spill beer into an amp with 1200 V on the plates???
:
: - j

I was working as an amp janitor at a music store when I accidentialy spilled a coke into a
twin reverb while the deck was sitting on top of the speaker/case. It broke into oscillation
and I turned it off quickly. Once the wet dried up it worked perfectly. I did not charge the
guy extra for that.

Phil Abbate




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John Stewart
 
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Sam Byrams wrote:

Phooey. A tube BASS amp needs to be a general purpose power amplifier,
not a guitar amplifier. Study true classics like the Altec 260B,
1570B, Mac MI200, and other audio amplifiers using real power
tubes,211s, 811s,812s, and up-look at a Varian Eimac catalog. If it
does not have at least 1200 vdc on the plates I am not interested at
all.


Imagination goes a long way, but then electrocution sets in!!!!!!

JLS


  #7   Report Post  
Jon Yaeger
 
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What happens when you spill beer into an amp with 1200 V on the plates???

- j





From: Lord Valve
Organization: EarthLink Inc. -- http://www.EarthLink.net
Newsgroups: rec.audio.tubes
Date: Sat, 03 Jul 2004 05:58:10 GMT
Subject: KT88 or KT90 for scratch built bass amp???



Sam Byrams wrote:

Phooey. A tube BASS amp needs to be a general purpose power amplifier,
not a guitar amplifier. Study true classics like the Altec 260B,
1570B, Mac MI200, and other audio amplifiers using real power
tubes,211s, 811s,812s, and up-look at a Varian Eimac catalog. If it
does not have at least 1200 vdc on the plates I am not interested at
all.


Play much on the road?

I didn't think so.

LV





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Karl Loon
 
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Jon Yaeger wrote in message ...
What happens when you spill beer into an amp with 1200 V on the plates???

- j


It it cold beer or warm.

K. L.




From: Lord Valve
Organization: EarthLink Inc. -- http://www.EarthLink.net
Newsgroups: rec.audio.tubes
Date: Sat, 03 Jul 2004 05:58:10 GMT
Subject: KT88 or KT90 for scratch built bass amp???



Sam Byrams wrote:

Phooey. A tube BASS amp needs to be a general purpose power amplifier,
not a guitar amplifier. Study true classics like the Altec 260B,
1570B, Mac MI200, and other audio amplifiers using real power
tubes,211s, 811s,812s, and up-look at a Varian Eimac catalog. If it
does not have at least 1200 vdc on the plates I am not interested at
all.


Play much on the road?

I didn't think so.

LV




  #9   Report Post  
Sam Byrams
 
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Two kinds of people will buy this amp: yuppies whose living rooms will
be its only habitat, and maybe a Stones-level touring act with
traveling techs. People who get electrocuted usually get it from the
115 VAC (or 220 in Europe) line supply, not the B+.

If a beer gets spilled in there the results will be the same as with
any tube box, just maybe more dramatic.
  #11   Report Post  
John Stewart
 
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Sam Byrams wrote:

Two kinds of people will buy this amp: yuppies whose living rooms will
be its only habitat, and maybe a Stones-level touring act with
traveling techs. People who get electrocuted usually get it from the
115 VAC (or 220 in Europe) line supply, not the B+.

If a beer gets spilled in there the results will be the same as with
any tube box, just maybe more dramatic.


Where does the liability begin & end if you should sell one of these
beasts & that is followed by an accident? Looks like a make work
project for the under employed law profession, to me anyway.

Good Luck, John Stewart


  #12   Report Post  
Sam Byrams
 
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Where does the liability begin & end if you should sell one of these
beasts & that is followed by an accident? Looks like a make work
project for the under employed law profession, to me anyway.


The same liability you have with any device-microwave oven or light
bulb-someone could abuse and possibly shock themselves with. Dead is
dead, and if it plugs into AC distribution voltage anywhere in the
world-100VAC is the lowest, in Japan-it can kill you. There's no magic
number a 6550 is under and an 813 over-the 400 volt B+ will kill you,
so will 1200. and the 1200 might kick you clear or burn the contacting
digit off whereas the 400 just might lock you up and fry you. Might,
might, might. If you are going to sell anything in the USA you could
wind up in court, but you will anyway, so do it right.

Dump a beer in there, there's going to be fireworks. But very few of
these things are going to be gigging at Bob's Country Bunker-bass
players don't need 500 watt amps anyway, they need the same amps and
efficient horn loaded speakers.
  #13   Report Post  
John Stewart
 
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Sam Byrams wrote:


Where does the liability begin & end if you should sell one of these
beasts & that is followed by an accident? Looks like a make work
project for the under employed law profession, to me anyway.


The same liability you have with any device-microwave oven or light
bulb-someone could abuse and possibly shock themselves with. Dead is
dead, and if it plugs into AC distribution voltage anywhere in the
world-100VAC is the lowest, in Japan-it can kill you. There's no magic
number a 6550 is under and an 813 over-the 400 volt B+ will kill you,
so will 1200. and the 1200 might kick you clear or burn the contacting
digit off whereas the 400 just might lock you up and fry you. Might,
might, might. If you are going to sell anything in the USA you could
wind up in court, but you will anyway, so do it right.

Dump a beer in there, there's going to be fireworks. But very few of
these things are going to be gigging at Bob's Country Bunker-bass
players don't need 500 watt amps anyway, they need the same amps and
efficient horn loaded speakers.


Thankyou for your carefully considered response.
Take it along with you when you try to buy liability insurance.

JLS


  #14   Report Post  
Sam Byrams
 
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Thankyou for your carefully considered response.
Take it along with you when you try to buy liability insurance.


Most boutique/High End vendors do not carry product liability
insurance. They couldn't afford the premiums, and underwriters are not
interested in businesses that small, and trial lawyers aren't
interested in companies without either known substantial PL coverage
or a very wealthy owner dumb enough to have incorporated himself in
any way which could be declared a personal holding corporation.
Winning a big verdict and being handed a set of factory keys is a
nightmare scenario for these sharks.

If they had to carry product liability insurance, most of the
boutique guitar vendors and High End audio companies would fold.

And it's doubtful insurance companies would be the least bit more
understanding of the plethora of products with open tubes with 500 vdc
plate voltages than they would be of a design with a caged,
interlocked tube with two or 3 kV. One shows intent to effectively
keep people away from HV and the other is an attractive nuisance-it's
a wonder no small children (that we know of) haven't been barbecued by
a shattered 6550 in a floor-sitting (boy is that stupid!) High End
amp.
  #15   Report Post  
Mark
 
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(OvrReactor) wrote in message ...
Anyone care to comment on which tube would be "better" for a high powered bass
amp? By "better", I mean more reliable when abused. You know how we bassists
are! I've been wanting to try my hand at building a high powered all tube bass
amp, but I figure someone else's experiences will help save me a lot of time
and money. I've built a few bass amps in the 100 to 200 Watt range, but I'd
like to take things up a few notches. And if I'm happy with the results, MAYBE
I might actually make a few for sale...

But I sure as heck couldn't call them "Mitchell Amps". People might think I'm
the "other" Tom Mitchell that made amps in Riverside, California back when I
was still in High School, and then people would expect me to FIX all those
bargain-basement Boogie clones...

By all means, POST your response, but PLEASE respond by EMAIL too! I;m only
drop in to this newsgroup two or three times a month.

Best regards,
Tom Mitchell
website -
http://members.aol.com/ecc81
website - http://www.over-reactors.com


Going higher in power will require custom transformers which will get
expensive. To double power, there is a 3 dB increase in volume e.g.
100 dB to 103 dB. The KT series are better than the conventional
numbers at an additional cost. For critical applications, the KT
versions are advised. For standard applications, the standard number
will work. If you insist on 200 watts, use transmitting valves. The
B+ will be 750 volts. The ceramic-metal outputs can be used but
remember the fins are connected to B+ and the MUST be fan cooled using
a socket made for fan cooling and the B+ MUST be delayed enough time
for the heater to get to full temperature (30 seconds). The size and
weight of the power transformers, heater transformer, reactors
(chokes) and output transformer will make a large amplifier very
heavy. A waist high steel rack cabinet with good quality wheels, two
chassis (power supply and amp connected by a cable) will be needed.

Power supply regulation is a must with bass! The current swing is high
so the B+ must not vary too much. A reactor input filter is highly
recommended. The ouput filter condenser should be large e.g. two 200
mfd, or higher, condensers in series (total voltage rating 1,5 times
the B+ voltage) with equalization resistors across them. The large
condenser value will keep the B+ more stable at high volume low pitch
frequencies. I know these work from extensive work in audio design.
Typical pi filters are fine for loads that do not vary greatly and
heater-cathode rectifiers give better voltage regulation than those
witha filament and also delay the B+ thus preventing cathode
stripping (greatly reduced valve life and shorts developing from the
cathode to G1).

I do not recommend using the 211 or 845 if you are going to be rough
with the amp. The tall envelope gives more surface area to get hit and
break. The filament is not designed for rough usage. These will also
require 1250 volts B+ for 100 watts output as well as a bias of about
100 volts thus a large signal is required for full output.

A stacked supply for 6550 is easier to work with than having dropping
resistors generating heat and the voltages from a stacked supply will
be enough to drive the screens and preamp stages. Two 300 volt
supplies with pi filters will work in this case. Keep the output
condenser large as above. The input condenser should be 20 mfd 450
volts (TVA1709). It is easier to find a pair of transformers with 300
volts output than 600 volts. They will also have the 5 and 6,3 volt
windings. The heater windings can be done a couple of ways, full-wave
center tap or two (ouput stage and preamp stages). Using filtered d-c
on the heaters WILL make a difference in the hum. D-c is MUCH better
than a-c for hum reduction/elimination.
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