No joy from the 50 watt Bluesmaster clone

[Mark]

Dear Blues,

I have been careful to use shielded cable where it is required, and place the non shielded wire in a place where it won't be effected by associated circuitry. The amp is surprisingly quiet.

It is thrown together for a reason. I didn't want to spend a lot of time making it look like a tidy amp to then realize a non HRM amp is more to my tastes. I will do a clean build of it once I've settled on the amp I like best.

I still have to try the amp with a Dumbleator in circuit. I like the tone the Dumbleator imparts.

I had a look at some old circuit diagrams of a Bluesmaster and voltages were as follows. B+1 = 422VDC, B+2 = 420VDC, B+3 = 391VDC, B+4 = 314VDC, B+5 = 306VDC.

I'm not sure these voltages are correct as I'd assume the B+1 to be more like 440VDC.

The voltages I have are vastly different from these voltages.

B+1 = 482VDC, B+2 = 480VDC, B+3 = 411VDC, B+4 = 370VDC, B+5 = 356VDC.

The voltages on the first stage of the amp are as follows; anode 218VDC, and cathode at 1.96VDC.

The second stage anode = 228VDC, cathode = 1.91VDC

The first OD stage anode = 225VDC, cathode 2.09VDC

The second OD stage anode = 228VDC, cathode = 2.01VDC,

The PI has 255.3VDC on the inverting side (82K plate), and 243.2VDC on the non inverting side (100K plate) the cathode voltage is 45.6VDC, the grid voltages are 28.5VDC (82K) and 29.9VDC (100K).

The voltage on the output tubes is anode 477VDC, screen 477VDC, grid (bias) -56VDC.

If I put a 100mV signal into the amp and switch the OD in and set the amp to "3" (my normal playing volume) the power supply B+1 drops to 475VDC. If I dime to amp to ridiculous levels "10" the rails down as follows; B+1 = 447VDC, B+2 = 415VDC, B+3 = 383VDC, B+4 = 344VDC, B+5 = 331VDC.

I estimate that if I change the PI dropping resistor to 7223 ohms and adopt the 15K and 10K values the PI and pre-amp voltage should be correct. The question remains what are the correct voltages on a Bluesmaster amp?

Thanks for reading my thread and your assistance.

[bluesfendermanblues]

Mark, your

- V1/first preamp tube and
- V2/second tube/OD-stage

voltages looks a little high

In a Bluesmaster

V1 should be 185-190V on pin1/6 anodes
V2 Should be around 200-205 V on pin 1/6

Increase the 22k resistor in the PSU or try different preamp tubes. I have found the EH ECC83 draws much less current than JJ ditto. Hence, the preamp voltages will be higher with EH and sound harder/brighter.

[Mark]

Man that was a quick reply Blues!

I have been using Groove Tube "Mullard copy" 12AX7M's as I had them lying around. Is there a preferred 12AX7 for these amps (excluding NOS $$$)?

I can get them for the purpose of fine tuning. I think I will have to adjust the power supply string values for sure. What would you expect on the PI of a Bluesmaster?

Thanks for all your help Blues.

[bluesfendermanblues]

Man that was a quick reply Blues!

I have been using Groove Tube "Mullard copy" 12AX7M's as I had them lying around. Is there a preferred 12AX7 for these amps (excluding NOS $$$)?

I can get them for the purpose of fine tuning. I think I will have to adjust the power supply string values for sure. What would you expect on the PI of a Bluesmaster?

Thanks for all your help Blues.

Hi Mark,

.....Anytime, glad if I can help.

Preamp tubes
The standard for V1 & V2 is JJ ECC83S
The standard for V3 (phase inverter) is Sovtek LPS.

(NOS: Mullards, RCA or Amperex for V1 and V2)

Poweramp tubes
EL34: Winged C (svedland) or EL34B from TAD
6L6: Winged C or NOS Sylvania STR (boogie standard in the 70s and 80s)

Bluesmaster PI voltage; I like 240-260V on anodes

[talbany]

Tony, I was just looking at installing the PAB switch.

I noticed one side of the relay lifts the earth connection from the mid pot, but the other side of the relay looks like it is shorting boths sides of the mid pot together, which doesn't make a whole lot of sense to me.

I dare say I must have it wrong.

Mark
Not quite sure what you are looking at there.. NC side of the relays have bottom of the mid pot to ground other side has bottom of the bass to mid wiper..

Updated Again ...Removed PCB for those that don't understand what's happening there..

Tony

[Structo]

Doesn't the BM have three relays?

OD, PAB and Mid Boost?

[talbany]

Doesn't the BM have three relays?

OD, PAB and Mid Boost?

Not in the one I did the layout with..

Tony

[Dr d]

If you are still having problems with a lack of gain, double check your grid resistor values and that you have got your cathode bypass resistors the in the correct order ie. 220/3.3 and 150/2.2. Its really easy to get these the wrong way round!!!

[wicker]

Did you checked all resistor and caps (non electrolytic) with mm ? I have caught few times myself that I have wrongly red color kode on resistors (not that problem when you're working with bulb light, especially to mistake orange and red ; ).

If still no joy, you can always give it to me

[Mark]

The input voltage to the non HRM overdrive has to be greater than the HRM overdrive as the 100K pre-set pot is set in roughly the same position (non HRM 25.53K, HRM 20K to 40K) but the HRM has more resistance in the resistive network.

The non HRM amp has a 220K resistor and a 100K pot (320K.)

I estimate that if 10vac were applied to the top of resistive string 798mV would be present at the grid of the first stage. So roughly 8% of the signal makes it to the OD stage.

The HRM amp has a 470K resistor, a 120K resistor and a 100K pot (690K.) If 10vac were applied to this resistive string a 20K value would deliver roughly 290mV, while a 40K value would deliver 579mV. Roughly 2.9% to 5.8% of the signal makes it to the first grid. The pot would have to be set to 55K to deliver the same signal as the non HRM amp.

I've done some "adjustments".

I've adjusted the rail voltages to Dumble specs, not any perceivable difference in tone (no reference to hear a difference either.)

I adjusted all the O.D. pots to the 11 o'clock position. This helped output and the amount of distortion on tap. When the middle and bass pots were set as per this thread with the treble at 45 degrees I found the cleans were much brighter than the distorted tones.

http://ampgarage.com/forum/viewtopic.php?t=12875

I also have a question about the PAB, what effect does virtually open circuiting the mid pot wiper to the top of the mid pot (bottom of bass pot)?

I would have thought simply lifting the earth connection from the mid pot would deliver the required boost?

[Mark]

If you are still having problems with a lack of gain, double check your grid resistor values and that you have got your cathode bypass resistors the in the correct order ie. 220/3.3 and 150/2.2. Its really easy to get these the wrong way round!!!

Thanks for the assistance, I checked the wiring and the leads are not the wrong way around. I find there is a good tone for rhythm work, but there isn't the gain on tap for soloing, the notes don't have a lot of sustain, and the amp doesn't easily feedback, the non HRM amp is a joy in that it does feedback easily, rolling the guitars volume control back delivers good rhythm tones.

I am of the opinion that the amp needs another gain stage and possibly a cathode follower as increasing the input the the overdrive (either increasing the pot beyond 45% \ or turning up the volume control to get greater gain) yields buzzy tone. I think the cathode follower would help with losses due to the tone stack.

I tried the recommended setting, but I found there weren't enough highs and I'd have to set the clean channel volume too high to get the gain I wanted which then made the clean channel louder the overdrive channel.

I found setting the input trimmer and the bass pot to 45 degrees \, the treble and mid trimmer to 45 degrees / seemed to deliver a Marshall like tone that wasn't buzzy. It is an aggressive tone which is cool too.

I can't but help think slotting part of a JCM-800 2203/4 pre-amp into the overdrive stage would work wonders.

http://tone-lizard.com/Ultimate_JCM800.htm

[talbany]

For those who think an HRM doesn't deliver gain on the OD side here is a clip of Rick Derringer playing an amp I built.. a 4X 6v stock HRM circuit PAB engaged plugged straight in..Also Craig Bartock Heart..100w HRM

http://www.youtube.com/watch?v=VNz2VhCJ3B0

Hope this helps!!

Tony

[guitardude57]

There still seems to be something going on there. You should have plenty of gain.....even though a blues master circuit.

Have you metered your solder connections? Even a .03 ohm continuity for a ground connection can wreck havoc.

If everything checks out.......... maybe you need to make a crunchier ODS with more gain.

Maybe you have what you have.... a blues machine.

[guitardude57]

Nice clip there Tony

You get no argument from me.

All these designs from HAD (and derivatives) can be coaxed into sing and grind.

Make it do what you want.

And Tony does a great job.

[talbany]

GD
I agree on HAD point!! Thanks for the kudos


Be Well!!

Tony