1 watt amp

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Bieworm
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1 watt amp

Post by Bieworm »

Hey Josh

Somebody asked me if I could build a 1W TMB amp. You reckon it's possible to make a 1W version of the tremolo TMB sans tremolo? Thinking single 12AU7 power tube...
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Re: 1 watt amp

Post by zaphod_phil »

Bieworm wrote:
Tue 05/04/21 7:10 am
Hey Josh

Somebody asked me if I could build a 1W TMB amp. You reckon it's possible to make a 1W version of the tremolo TMB sans tremolo? Thinking single 12AU7 power tube...
Take a look at Thundertweak's Heavy Watter amp, which uses a single 12AT7 in push-pull. Then maybe just use that with the Superlite TMB's preamp.

BTW I've seen reports of 12AU7 power amps sounding dull, FWIW
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Re: 1 watt amp

Post by TriodeLuvr »

zaphod_phil wrote:
Tue 05/04/21 10:16 am

BTW I've seen reports of 12AU7 power amps sounding dull, FWIW
Triode outputs probably aren't so good for guitar amps. Power pentodes produce a higher level of distortion, in particular IMD. This creates an edge to the sound that can make it seem more detailed. Once you get used to that, cleaner amplification sounds somewhat lifeless. For low power, I would stay with pentodes but move to a single-ended topology. The 5686 (2.7 W) or 6AK6 (1.1 W) might be a good choice. Both of tubes also have a separate connection for G3 (suppressor), so they can be wired as a "pseudo-real" triode (G2 and G3 connected to anode) for comparison.

Jack
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Re: 1 watt amp

Post by zaphod_phil »

TriodeLuvr wrote:
Tue 05/04/21 1:35 pm
zaphod_phil wrote:
Tue 05/04/21 10:16 am

BTW I've seen reports of 12AU7 power amps sounding dull, FWIW
Triode outputs probably aren't so good for guitar amps. Power pentodes produce a higher level of distortion, in particular IMD. This creates an edge to the sound that can make it seem more detailed. Once you get used to that, cleaner amplification sounds somewhat lifeless. For low power, I would stay with pentodes but move to a single-ended topology. The 5686 (2.7 W) or 6AK6 (1.1 W) might be a good choice. Both of tubes also have a separate connection for G3 (suppressor), so they can be wired as a "pseudo-real" triode (G2 and G3 connected to anode) for comparison.

Jack
Coincidentally, I had just been thinking of the 6AK6 earlier today, but being lazy, didn't get round to suggesting it :)
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Re: 1 watt amp

Post by Bieworm »

I found the guytronics Gilmore JR a very interesting amp. It's got a 6N1P output tube.

Check this: https://youtu.be/6oDY0cBUtac
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Re: 1 watt amp

Post by Daviedawg »

6N1P output works well. I have an amp with one which sits in the cupboard and gets the occasional exercise. I quite like it but of course it is always running near the red line as it were. Fine for recording though.
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Re: 1 watt amp

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Daviedawg wrote:
Wed 05/05/21 2:31 am
6N1P output works well. I have an amp with one which sits in the cupboard and gets the occasional exercise. I quite like it but of course it is always running near the red line as it were. Fine for recording though.
Dd
That's what the client's looking for..
Was also looking into the marshall JTM1. I would prefer to build that one, but the PT on the schematic calls for 12.6VAC filament voltage. I can only score 6.3V types ..preferably the Hammond 369EX.
What also puzzles me on that schematic is the center tap of the heaters at the 12AU7. It's connected to the cathode of the tube, but there are no resitors between heaters and cathode..is that normal? Any idea how to approach this with a 6.3V secondary?
heaters center tap.pdf
Marshall 1 watt amp revised JTM1.gif
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Re: 1 watt amp

Post by TriodeLuvr »

There are indications in this schematic that the designer had difficulties with hum. There's no need to use a 12V winding. Use a 6.3V winding and add an artificial CT if necessary using a couple 47 ohm resistors across the winding. Wire all the tubes for 6.3V operation as normal with heater pins 4 and 5 connected together and power applied between 4/5 and pin 9. Instead of connecting heaters to the output tube cathodes, elevate the CT to +50V or so with a resistive divider to B+. I would also connect the main power supply ground (negative output of the bridge rectifier) directly to the chassis and use that as a star ground. Use an audio grade power transformer with a flux band if possible.

Jack
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Re: 1 watt amp

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TriodeLuvr wrote:
Wed 05/05/21 11:48 am
There are indications in this schematic that the designer had difficulties with hum. There's no need to use a 12V winding. Use a 6.3V winding and add an artificial CT if necessary using a couple 47 ohm resistors across the winding. Wire all the tubes for 6.3V operation as normal with heater pins 4 and 5 connected together and power applied between 4/5 and pin 9. Instead of connecting heaters to the output tube cathodes, elevate the CT to +50V or so with a resistive divider to B+. I would also connect the main power supply ground (negative output of the bridge rectifier) directly to the chassis and use that as a star ground. Use an audio grade power transformer with a flux band if possible.

Jack
You mean bridge the heater wires with a 47R resistor? What is the purpose? And where is the resistor best positioned? At the PT?
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Re: 1 watt amp

Post by TriodeLuvr »

The artificial center tap is only used when the transformer's filament winding has no center tap. I think this is described on the Valve Wizard site. The drawing below shows it grounded, but it's beneficial to elevate the heaters by connecting it to a positive voltage instead.

http://www.valvewizard.co.uk/heater.html

Image

Jack
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Re: 1 watt amp

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Ok.. you mean an artificial center tap. I thought you meant a single resistor bridging the wires... that was odd to me
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Re: 1 watt amp

Post by Daviedawg »

A friend of mine asked me to build a JTM1. In the end it worked out great but it took a lot of post build work to get it right. If I have any notes I will see if there is anything meaningful there which I can post.

Dd
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Re: 1 watt amp

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Daviedawg wrote:
Thu 05/06/21 2:11 am
A friend of mine asked me to build a JTM1. In the end it worked out great but it took a lot of post build work to get it right. If I have any notes I will see if there is anything meaningful there which I can post.

Dd
That would be great Dd

Did you work with the Matec Schematic?
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Re: 1 watt amp

Post by Bieworm »

On the schematic the cathode of V1a has a bypassed bias resistor that's parallelled with an RC.. is that something that is applied more often?
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Re: 1 watt amp

Post by TriodeLuvr »

Bieworm wrote:
Thu 05/06/21 7:56 am
On the schematic the cathode of V1a has a bypassed bias resistor that's parallelled with an RC.. is that something that is applied more often?
Some type of frequency contouring. Would you like me to run a simulation on it? I could post a graph of the response it creates.

Jack
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