1 watt amp

Forum to discuss amp circuits besides the 18 Watters and their ilk.

Moderators: JMPGuitars, CurtissRobin, colossal, zaphod_phil, Daviedawg, Graydon

User avatar
Bieworm
Verbose Moderator
Verbose Moderator
Posts: 2287
Joined: Mon 02/10/20 8:24 am
Location: Belgium

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...
0 x
"THIS should be played at high volume..preferably in a residential area"

User avatar
zaphod_phil
Builder, Admin
Builder, Admin
Posts: 15208
Joined: Wed 03/19/03 2:00 am
Location: YYZ

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
2 x
Nature abhors a clean tube amp

User avatar
TriodeLuvr
Frequent poster
Frequent poster
Posts: 616
Joined: Tue 10/16/18 11:19 am

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
0 x

User avatar
zaphod_phil
Builder, Admin
Builder, Admin
Posts: 15208
Joined: Wed 03/19/03 2:00 am
Location: YYZ

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 :)
1 x
Nature abhors a clean tube amp

User avatar
Bieworm
Verbose Moderator
Verbose Moderator
Posts: 2287
Joined: Mon 02/10/20 8:24 am
Location: Belgium

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
0 x
"THIS should be played at high volume..preferably in a residential area"

Daviedawg
Superior Amp Tech
Superior Amp Tech
Posts: 748
Joined: Fri 01/08/10 2:00 am
Location: Scotland

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.
Dd
0 x

User avatar
Bieworm
Verbose Moderator
Verbose Moderator
Posts: 2287
Joined: Mon 02/10/20 8:24 am
Location: Belgium

Re: 1 watt amp

Post by Bieworm »

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
You do not have the required permissions to view the files attached to this post.
0 x
"THIS should be played at high volume..preferably in a residential area"

User avatar
TriodeLuvr
Frequent poster
Frequent poster
Posts: 616
Joined: Tue 10/16/18 11:19 am

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
1 x

User avatar
Bieworm
Verbose Moderator
Verbose Moderator
Posts: 2287
Joined: Mon 02/10/20 8:24 am
Location: Belgium

Re: 1 watt amp

Post by Bieworm »

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?
0 x
"THIS should be played at high volume..preferably in a residential area"

User avatar
TriodeLuvr
Frequent poster
Frequent poster
Posts: 616
Joined: Tue 10/16/18 11:19 am

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
0 x

User avatar
Bieworm
Verbose Moderator
Verbose Moderator
Posts: 2287
Joined: Mon 02/10/20 8:24 am
Location: Belgium

Re: 1 watt amp

Post by Bieworm »

Ok.. you mean an artificial center tap. I thought you meant a single resistor bridging the wires... that was odd to me
0 x
"THIS should be played at high volume..preferably in a residential area"

Daviedawg
Superior Amp Tech
Superior Amp Tech
Posts: 748
Joined: Fri 01/08/10 2:00 am
Location: Scotland

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
2 x

User avatar
Bieworm
Verbose Moderator
Verbose Moderator
Posts: 2287
Joined: Mon 02/10/20 8:24 am
Location: Belgium

Re: 1 watt amp

Post by Bieworm »

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?
0 x
"THIS should be played at high volume..preferably in a residential area"

User avatar
Bieworm
Verbose Moderator
Verbose Moderator
Posts: 2287
Joined: Mon 02/10/20 8:24 am
Location: Belgium

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?
0 x
"THIS should be played at high volume..preferably in a residential area"

User avatar
TriodeLuvr
Frequent poster
Frequent poster
Posts: 616
Joined: Tue 10/16/18 11:19 am

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
1 x

User avatar
Bieworm
Verbose Moderator
Verbose Moderator
Posts: 2287
Joined: Mon 02/10/20 8:24 am
Location: Belgium

Re: 1 watt amp

Post by Bieworm »

TriodeLuvr wrote:
Thu 05/06/21 8:18 am
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
Would be nice.. yes👍
Marshall 1 watt amp revised JTM1.gif
The circuit attached to the mains power inlet ground.. is that a noise filtering system? I am using a filtered IEC plug, so I reckon it's obsolete?
You do not have the required permissions to view the files attached to this post.
0 x
"THIS should be played at high volume..preferably in a residential area"

User avatar
TriodeLuvr
Frequent poster
Frequent poster
Posts: 616
Joined: Tue 10/16/18 11:19 am

Re: 1 watt amp

Post by TriodeLuvr »

I had a discussion yesterday on a different forum regarding that ground network. It's intended to break ground loops caused by the parallel currents in the house (earth) grounding system. Personally, I think it's a bad idea, and I don't quite understand how it would be beneficial in a system with only one component, such as a guitar amp. Anyway, there's a brief description of a similar network here:

https://www.tubecad.com/2017/09/blog0397.htm

Jack
2 x

User avatar
TriodeLuvr
Frequent poster
Frequent poster
Posts: 616
Joined: Tue 10/16/18 11:19 am

Re: 1 watt amp

Post by TriodeLuvr »

Here's the sim of the JTM1 input circuit. Be sure to consider the scale on the left when viewing the plot. The contour is very mild, not sure why they even bothered. Note that the shallow rolloff above 10K is the result of the 100pF cap from anode to cathode. It's mostly an ultrasonic filter.

Jack

Image
0 x

Daviedawg
Superior Amp Tech
Superior Amp Tech
Posts: 748
Joined: Fri 01/08/10 2:00 am
Location: Scotland

Re: 1 watt amp

Post by Daviedawg »

"Did you work with the Matec Schematic?" Bieworm.

If that is the schematic you posted above, then yes. I have looked through my stuff on it. I had a notion that I had made changes but that must have been something else because it worked as drawn as far as my notes say. It is fitted with an Ampmaker OT and toroidal PT and three NOS Brimars.

The guy is still using it as his home amp.

Dd
1 x

Daviedawg
Superior Amp Tech
Superior Amp Tech
Posts: 748
Joined: Fri 01/08/10 2:00 am
Location: Scotland

Re: 1 watt amp

Post by Daviedawg »

"The circuit attached to the mains power inlet ground".

There was discussion of that on the site where I found the schematic. I did not incorporate it in my build.

Dd
0 x

Post Reply