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 Post subject: First amp finished.
PostPosted: Dec Sat 19, 2020 1:01 am 
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Location: Cave Springs, AR
Some time back I inquired about running a 5V rectifier tube on 6.3v.

Here's why. This is my brother's Christmas present, a blacked out AR-15 themed amp for the office area of his wood shop. He has a SS Bluetooth amp now that he uses with his phone. I have a switched outlet on the back for an Esinkin Bluetooth adapter. It is built in an 8x10x2-1/2 aluminum chassis. That doesn't sound too bad until you decide to put all the iron underneath. A pair of 6J5s drive the 6V6s.

The ON/OFF is an "adapted" genuine AR-15 SAFE/FIRE switch. The volume knob is a genuine AR-15 flash hider "adapted" to a 1/4" pot. It is surrounded by a piece "adapted" from a genuine AR-15 quad rail hand guard. The side rails are "adapted" from AR-15 style carry handles but are actually made for AR-15 looking Air-soft guns. I couldn't afford $30+ EA for genuine AR carry handles. ("adapted" = don't ask)

It is largely based on the Lacewood 1&2 amps but I also stole some ideas from pbpix here on ARF. I liked his use of the CL-90 to ramp up the B+ while the tubes were heating.

Voltages were taken by a DMM and the current was across a 10A (close enough to) 1 Ohm resistor.

I did a single channel mock up and tried multiple typologies, screen resistors, bias resistors, B+ voltages, ETC. A tone generator showed my input - pre-amp - final sine waves on my scope (2 at a time).

It was quite the learning experience. So long as you don't exceed the tubes limits you can get quite acceptable if not great performance.

This thing rocks and can get a little loud for an office or bedroom amp. It really liked my Klipsh CF1s but he ain't getting them. He has some bookshelf speakers similar to the metal KLHs right now. It did OK with my set of KLHs but much better with my Bose 201 III. I may let him audition them.

This amp provides exactly what I wanted. I'm sure there are guys here that could "improve" it. But I don't see how.

BTW Here's an all new example of "Tube Matching!"

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 Post subject: Re: First amp finished.
PostPosted: Dec Sat 19, 2020 1:23 am 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: New Hampshire, USA
Very cool! Looks very nice.


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 Post subject: Re: First amp finished.
PostPosted: Dec Sat 19, 2020 2:11 am 
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Joined: Jul Fri 18, 2008 10:02 am
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Location: near ST Louis Mo 62002
Looks very nice Mark , now make a crystal set for a signals source .

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 Post subject: Re: First amp finished.
PostPosted: Dec Sat 19, 2020 8:11 am 
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Location: Arvada, CO, 80004
Beautiful!!!!

And who says that tubes must be made of glass to make a warm sound?! Audiophools :P

Really did a hum-dinger job on it. I remember you asking about an all metal rectifier tube too...

Anywho, I think you did a wonderful job, and should last ages.

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 Post subject: Re: First amp finished.
PostPosted: Dec Sat 19, 2020 8:33 am 
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Joined: Jun Sat 15, 2019 7:43 pm
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That 2 amp CL-90 will never get hot enough to give you full B+

DM


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 Post subject: Re: First amp finished.
PostPosted: Dec Sat 19, 2020 1:24 pm 
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Location: Utica, NY 13502 (USA)
With no volume control at the input to the 6J5, you could have distortion on peak excursions.

Dave


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 Post subject: Re: First amp finished.
PostPosted: Dec Sat 19, 2020 4:16 pm 
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devilsmist wrote:
That 2 amp CL-90 will never get hot enough to give you full B+

DM


Works fine.

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 Post subject: Re: First amp finished.
PostPosted: Dec Sat 19, 2020 4:35 pm 
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battradio@ wrote:
Looks very nice Mark , now make a crystal set for a signals source .


Stereo? :D

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 Post subject: Re: First amp finished.
PostPosted: Dec Sat 19, 2020 5:35 pm 
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That's really good looking!


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 Post subject: Re: First amp finished.
PostPosted: Dec Sat 19, 2020 7:25 pm 
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err ducks wrote:
devilsmist wrote:
That 2 amp CL-90 will never get hot enough to give you full B+

DM


Works fine.

So, you have a 2 amp load on the B+?? Without a proper load as specified for the CL-90 all you have is a resistor not a thermistor.

DM


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 Post subject: Re: First amp finished.
PostPosted: Dec Sat 19, 2020 7:39 pm 
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err ducks wrote:
battradio@ wrote:
Looks very nice Mark , now make a crystal set for a signals source .


Stereo? :D


OF course or bi-amped speaker , :D :D

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 Post subject: Re: First amp finished.
PostPosted: Dec Sat 19, 2020 9:42 pm 
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devilsmist wrote:
err ducks wrote:
devilsmist wrote:
That 2 amp CL-90 will never get hot enough to give you full B+

DM


Works fine.

So, you have a 2 amp load on the B+?? Without a proper load as specified for the CL-90 all you have is a resistor not a thermistor.

DM


I didn't realize that they had a minimum load.

I did a little 'speriment. With CL-90 it takes about 6 seconds for full B+, with the CL-90 jumped out it takes ~ 2 Sec.

Is the added R in the RC responsible for the difference?

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 Post subject: Re: First amp finished.
PostPosted: Dec Sat 19, 2020 10:54 pm 
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With a (100%) 2 amp load it will drop down to 1.18 ohms resistance. At 1/2 amp it is only down to 7.8 ohms, the resistance goes up as the load decreases. If it is giving you the desired delay, with the desired drop in voltage that is fine but you will lose some B+ voltage. Nice looking build :)
Here are the spec's for the CL-90 and the percentages of resistance at various loads.
https://www.mouser.com/datasheet/2/18/A ... 315885.pdf

DM


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 Post subject: Re: First amp finished.
PostPosted: Dec Sat 19, 2020 11:07 pm 
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Location: Cave Springs, AR
devilsmist wrote:
With a (100%) 2 amp load it will drop down to 1.18 ohms resistance. At 1/2 amp it is only down to 7.8 ohms, the resistance goes up as the load decreases. If it is giving you the desired delay, with the desired drop in voltage that is fine but you will lose some B+ voltage. Nice looking build :)
Here are the spec's for the CL-90 and the percentages of resistance at various loads.
https://www.mouser.com/datasheet/2/18/A ... 315885.pdf

DM



Thanks for the info. I am getting some delay and the B+ is right where I want it so all is good!

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