New Amplifier Design - "Murder One" - Submini Pentode, Low Voltage

[iccaros]

Hi Rick.

Right then. I've got most of the Parts in stock to build the modders delight version.
I'm just struggling to get the 2 watt 18r resistors. I can find 3 watt 18r resistors, can I use these?
I can also get 1.6 watt 18r resistors if that's any better?

Also what values should I be experimenting with r13a?
And finally where in the UK (Lincolnshire) are you getting the d bar handles to protect the tubes?
I can't find any anywhere near small enough.

Thanks in advance
Michael

3 watt is just fine (better even if it fits your case) , 1.6 watt may work but you need to do the math, rick is dropping about 5.7 (12 - 5.7 = 6.3 volts, what the these tubes like on their heaters) volts so ohms law says V = I *R or V/I = R in this case, according to the datasheet the heater will pull .3 amps

Rick got 18 ohms I assume from doing the math of dropping 5.7 volts  =  5.7/.3 = 19 ohm (18 is close enough and probably the closest standard value)
using what we have v = I * R or V = .3 * 18 = 5.4 volts
to find wattage ,there are a few formulas but this works
Watts Law   Power = Voltage * Current
5.4*.3 = 1.62 watts
The other way is P = I^2 * R
.3^2 * 18 = 1.62 watts 

so all of that to say 1.6 would work, but you would be at the limit of that resistor and could have issues, It a rule of thumb to go x2 as big, Rick decided that 2watts was enough and it works for him every time as far as I know.


hope that helps

[frequencycentral]

^^^

Yup, I concur.

The roll bars sre from B&Q. 

I'm using a newer layout these days, without the stuff for the bias switch, which was a hangover from earlier versions. I'll post it up later.

[Haynesarama]

Hi Steve and Rick.

Thanks for your speedy responses

Steve cheers for putting your time in to do the math,
That's it then 18r 3watt resistors ordered, I'm good to go once
Everything arrives

Rick I'll look forward to seeing your updated files,
I should learn to be more patient, I've just etched myself
Your modders delight board from page 14! Lol

Now to grab some of those pesky roll bars!
I'll keep you all posted.

Cheers
Michael

[frequencycentral]

This is the layout I've been using for a while, verified. Version 7 - I'm such a tweaker. It dispenses with the bias switch and associated circuitry. It also includes (orange) pads and swiching diagram for adding a pre-out using the existing speaker out socket - it basically takes a tap from the preamp stage and also cuts power to the pentode when switche to pre-out mode. If you dont want the pre-out switch you'll need to jumper the orange pads together.

BTW, it's easy to build teh Modder's Delight without the bias switch, just a matter of not using a few components and wiring it slightly differently.

[askwho69]

where can i order 6111, 5672 and the 1750a transformer same site? anyone? if i order piece by piece it will cost me shipping please anyone?

A2

Thank you so much God for bringing Rick Holt in this forum

God Bless

[frequencycentral]

Small Bear sell 6111 and 5672.

Thank you so much God for bringing Rick Holt in this forum

[Govmnt_Lacky]

I might be a bit dense Rick but.... where is the circuit Output 

I see the input, I see power and ground, I see your switching diagram but, I am still missing where the signal is coming from to go to the Output jack.

When the switch is one way, the signal is coming from the Transformer (red wire) and when it is the other wsay, it is coming from the Volume pot (green line)

Do these wires get removed from the board and soldered to the switch? Do those holes then get left open?

Sorry if I am a little dumb!! Working long hours this week 

[iccaros]

the two transformer outputs.

I do not see the loading for the transformer, but that may be a single load transformer I have not looked it up

[Blackface007]

This is the layout I've been using for a while, verified. Version 7 - I'm such a tweaker. It dispenses with the bias switch and associated circuitry. It also includes (orange) pads and swiching diagram for adding a pre-out using the existing speaker out socket - it basically takes a tap from the preamp stage and also cuts power to the pentode when switche to pre-out mode. If you dont want the pre-out switch you'll need to jumper the orange pads together.

BTW, it's easy to build teh Modder's Delight without the bias switch, just a matter of not using a few components and wiring it slightly differently.

Hi Rick,
I built "Murder One V7" using 6112 as preamp. It sound pretty cool, especially if I crank it. But up to 50% Gain it start to "motor booting" or almost "vibrato" altough I do not use LFO like your "Vibracaster". Any advise to eliminate the "motor booting"? Should I icrease the C15 (10µf) or R10 (1.8 K)? Or is it enough to change the tube preamp to 6111? I'm still waiting of my 6111.
Thanks

[frequencycentral]

Nice. 6112 is like twice the gain of 6111. It will require higher anode resistors ( R1, R2 - try 100k) and probably a higher value grid stopper ( R12 - try 470k).

If it still motorboats after changing those value, try cutting the HV trace between C12 and R1/R2 and bridging the cut trace with a 22k resistor. For completeness, also consider adding another 10uF 100v cap between R1/R2 and ground. Basically, cutting the trace, bridging it with the resistor and adding the extra cap is creating a B1 (to the 5672's B+), really you're converting the preamp section to a Superfly preamp.

BTW, I've got a few spare etched PCBs and tube sets if anyone wants one.

[Blackface007]

Nice. 6112 is like twice the gain of 6111. It will require higher anode resistors ( R1, R2 - try 100k) and probably a higher value grid stopper ( R12 - try 470k).

If it still motorboats after changing those value, try cutting the HV trace between C12 and R1/R2 and bridging the cut trace with a 22k resistor. For completeness, also consider adding another 10uF 100v cap between R1/R2 and ground. Basically, cutting the trace, bridging it with the resistor and adding the extra cap is creating a B1 (to the 5672's B+), really you're converting the preamp section to a Superfly preamp.

BTW, I've got a few spare etched PCBs and tube sets if anyone wants one.



Thanks a lot Rick for your answer.

how to have the pcb Rick?

Regards

[Blackface007]

If it still motorboats after changing those value, try cutting the HV trace between C12 and R1/R2 and bridging the cut trace with a 22k resistor. For completeness, also consider adding another 10uF 100v cap between R1/R2 and ground. Basically, cutting the trace, bridging it with the resistor and adding the extra cap is creating a B1 (to the 5672's B+), really you're converting the preamp section to a Superfly preamp.

should I put 22K (cutting HV trace) before connection to transformator or after?

Thanks again Rick
Regards

[frequencycentral]

I'd put it immediately before R1/R2. Say roughly parallel with the 6112.

[Blackface007]

I'd put it immediately before R1/R2. Say roughly parallel with the 6112.

Thanks a lot Rick. I have to do it tommorow night, because I don't have the right value for R1/R2 and R12. I let you know the result.

[Blackface007]

Nice. 6112 is like twice the gain of 6111. It will require higher anode resistors ( R1, R2 - try 100k) and probably a higher value grid stopper ( R12 - try 470k).

If it still motorboats after changing those value, try cutting the HV trace between C12 and R1/R2 and bridging the cut trace with a 22k resistor. For completeness, also consider adding another 10uF 100v cap between R1/R2 and ground. Basically, cutting the trace, bridging it with the resistor and adding the extra cap is creating a B1 (to the 5672's B+), really you're converting the preamp section to a Superfly preamp.

BTW, I've got a few spare etched PCBs and tube sets if anyone wants one.

Hi Rick,
I use 120 K Ohm for R1/R2 and 510K for R12, also applied C12 and 10 µF. The sound is much better, "motor boating" can be eliminated, if I crank it can be very cool. Now I come to the next problem, the sound is cutted earlier as I expect, i.e. if I pick string E Low, the "sustain" is stopped much earlier (even earlier than a Django style guitar). After picking a string the sustain makes hingher volume and suddenly (millisecond) niose and than stop. Any suggestion? Bad tube maybe ?
Regards

[zambo]

Im not Rick, but it sounds like it could be a cold solder joint.

[Blackface007]

Im not Rick, but it sounds like it could be a cold solder joint.

Hi Greg,
thanks a lot for the suggestion. I'll check (resorder) it.
Regards

[Blackface007]

Im not Rick, but it sounds like it could be a cold solder joint.

Hi Greg,
thanks a lot for the suggestion. I'll check (resorder) it.
Regards

Thanks a lot Greg and Rick. I have soldered the 6112 and 5672 directly into the board without IC socket. Now, it sounds really great for me. I love it; cranked sound. I need to learn more the theory tube before I go to the next..... project.

[zambo]

Awesome!    gonna post a clip?

[bluebunny]

Put this together today (thanks for the board, Rick) and was just trying it out.  Not boxed or anything just yet, but jury-rigged on my desk to a spare (4R) speaker.

Gets nice and warm and the 6111 glows reassuringly.  But I notice I get an unexpected tremolo when the gain is past 8 or 9 and as the signal fades out (i.e. not noticeable when played continuously hard, only when the signal fades).  Any ideas?

My PSU is giving 11.7V (IC1 pins 1 & 8).  I notice the B+ is oscillating gently between about 61V and 62V (somewhere between 1 and 2 Hz?).  Does any of this sound right?