Thanks for the feedback! I appreciate it. I guess I will just leave it as is, with the 2.2K dropping resistor on the PI.
Unless there is any benefit I am missing of having the voltages higher (ie PI at 300V)?
Dropping the 2.2k to a 1k will only buy you a few more volts.So forget about trying to get 300V from that transformer!.Are you going to notice a big difference in tone from a few volts?. I don't know did you notice a big difference when you went from the Mullard to the Fender AX?. Probably not. Unless you plan on running the amp wide open for long periods of time and am really concerned about headroom. Chances are your 6V's will break up long before your PI does anyway!
Again NO!
Tony
Many thanks again Tony. It is comforting to read and I will leave as is!
Just to make sure I understood if I reduce the PI dropping resistor all the way to 470R for example again I will be just gaining a few more volts and increasing the headroom of the PI a bit and the tonestack by consequence, therefore not much difference in tone specifically because the power tubes with probably go in overdrive before the PI anyway
For this amp my initial idea was to have a lower wattage that can be really pushed with master at Maximum on a small club but still playable without being too sterile at home with master at 1 o’clock. So far it is doing the intended.
Just a curiosity when I first got it up and running I had a 820R dropping resistor in place of the 22K, therefore with much higher voltages on the stack (around 270V-280V). I did it as an experiment but did not like the sound of the amp on that configuration. It was very harsh and unbalanced. I feel the Dumble design is best at lower voltages...once I added the 22K the amp came back to life and sounded at its best.
In Most of the Dumbles, I have seen V1 can vary anywhere from 185 to 205. Some people seem to like the lower voltages and the purists insist 200V on the money?. Which is right? I have no clue it's really up to your ears!. We need to remember, preamp tubes are cathode biased so depending on the current draw of that tube you can get wild swings in voltages of up to and sometimes exceeding 10 Volts (as you know).
There are plenty of people here and on the net that say they really prefer the sound of 1 tube over the other and then say brand X sounds better to them than brand Y. This could very well be due to current draw of that tube they prefer bias's up right in the sweet spot of the curve that they like in that particular amps power supply because 10 volts can be rather noticeable especially in an amp with cascading gain stages!.
BTW.. Cathode biased output tubes are no different like an EL-84 Vox style or a Tweed Fender 6V/L can too be rather noticeable!
So to answer your questions. For your situation Yes I would shoot for the lower end of the voltages. I generally don't like to go below 1k on my droppers to try to keep my nodes somewhat isolated!..Also unless you carry around a meter and a variac or get a separate power supply, your going to run into all kinds of AC voltage swings in the clubs you will be playing which I've found generally swings from 110 (at worst) to 123 (at worst) this will throw the bias off every tube inside your amp
Tony
" The psychics on my bench is the same as Dumble'"
Very insightful Tony, many thanks for taking the time. I actually noticed almost 20V swing between a groove tubes Fender 12AX7 and a RCA long Black plate angled d getter on V1.
A naive question maybe but is there a relationship between gain and voltage or frequency response and voltage? For example does increasing 10V will make the amp sound more trebly. The reason I ask is because everytime I had the newer tubes (with higher voltage) it always sounded less smooth and more trebly to me, but I thought it was the old vs new thing rather than the actual Voltage...
Thanks for the tip on aiming for the lower end of the voltages. On my amp for each position I tried a few different tubes until I settled on a favourite. I consistently preferred older tubes than newer and afterwards when I checked the result was always a lower voltage so I guess would be silly to increase it (by reducing the PI dropping resistor) on my amp.
I actually really like how the amp sounds now and although I only had a late 70’s Lab Series L5 and a 90’s Fender Custom Shop Dual Professional to benchmark it against I unfortunately have no other Dumble style for a comparison.
You do not have the required permissions to view the files attached to this post.
You will find that (in general) Most of the NOS tubes (Mullard,RCA,Funkin etc) we use will draw more current than the newer Chinese versions. Your question regarding voltage/ frequency response is not an easy one to answer in a quick post because there are many factors to consider when discussing plate characteristics.Here is a paper explaining load lines and how it might affect tone. I recommend reading this along with Miller capacitance
I cannot say for certain if the NOS tubes you have sound different because they draw more current than the newer tubes or if it is how the tube was manufactured and the materials used.My guess would be probably both.
However I will say that in general with most 12Ax's you might get this when you lower your plate voltages on V1 and V2 using the same tube.
1.less headroom
2.looser low end
3 less treble
4 softer feel
5 Change in harmonic structure
BTW. Just so we are clear...Preamp tubes are used for signal amplification, not power amplification, and the side effects of cathode biasing are not quite as important as power tubes but still can be noticeable when tube rolling in the same amp.
Tony
" The psychics on my bench is the same as Dumble'"
Just a further questions:
My power supply has different options of 220V, 230V, 240V. In the Uk (as most of Europe) is 230V. Would it be unsafe to try to run the amp at the alternative 220V, 240V just to simulate the “wall” variations you mentioned and see how different the amp will sound when the PT is a bit starved (like EVH) or a bit hot.
It's worth being aware that UK (and elsewhere) mains can be quite variable (+/- 10%), depending on where you live also, eg. city or countryside. Ours is 245V quite often. If you set it to 220V then you are going over by a good bit, particularly once it has been rectified.
Check your mains supply on a regular basis at different times of the day to get an idea of what you are dealing with.
For a given mains input voltage, the 240V option will produce the lowest B+ and filament voltages. Here in the states a PT will often have the choice between 120V and 125V primary selection. I always use the 125V selection in order to provide a lower B+ and filament voltage. My mains voltage is usually 122-123V, occasionally 125V, and sometimes 120V during heavy usage hours.
This in an industry that I work in from time to time so I am very familiar with the regulations here in the U.K.
Just for interest here is an explanation of the U.K. Supply
Voltage optimisation
Voltage optimisation is a term commonly used to refer to the energy-saving technique of reducing the electricity voltage supplied to a site, in order to reduce losses in the equipment, thereby reducing energy consumption, CO2 emissions and the electricity costs. The lifetime of the equipment is also extended, because it generally runs cooler at the reduced voltage, with a consequent reduction in maintenance costs.
Most electrical equipment is designed to operate with voltages within the standardised levels (with an allowance of 4% for losses within the installation), so many items of equipment are supplied with a higher voltage than is required for satisfactory operation.
Just as it was in 1960, the supply voltage to domestic properties in the UK is still nominally 240 V AC at 50 Hz, although the declared voltage in the UK is now 230V AC +10% to -6%. Historically the domestic voltage was 240 V +/-6% (and 415V 3phase), whilst continental Europe was 220V (380V 3 phase). Since 1995 the nominal voltage across Europe has been 230V (400V 3 phase).
In practice nothing has been changed in the UK. The first stage of European voltage harmonisation required a supply voltage of 230 V of -6% to +10%, i.e. be between 216.2 to 253V from a starting point of 240V +/-6%, i.e. be between 225.6 to 254.5V.
The second stage of European harmonisation was due to happen from 1st January 2003. This was 230V +/-10%, i.e. to be between 207 to 253V. The second stage has still not been applied, as of April 2013. So the situation in the UK regarding supply voltage, stated in law is that it should be 230V -6% +10%.
It is not unusual for the supply voltage to vary substantially throughout the day. The average voltage in the UK is around 242V. This means that in the majority of properties, electrical equipment is running at a voltage much higher than needed, resulting in excessive losses in many types of equipment. This is due, in a large part that due to the so called harmonisation of supply voltages in Europe all new low voltage appliances are designed to operate at 230V or even 220V. Therefore it can be seen that much equipment designed to be operated at 230V and 220V may be being supplied with a voltage above this if we consider that the UK average supply voltage is 242V, much higher than is needed.
230v is now considered standard in Australia as well, with -10% +5% tolerance.
I built an amp for someone using vintage transformers and when he played the amp, the volume would go up and down. He brought it to me to fix and it would never do it. Drove us both crazy.
After the third time I went up to his place and noticed his lights would flicker. His power would fluctuate every 10-15mins, drop down to about 220v-225v. Cause the transformer was rated for 240v you would hear every time the power dropped! Swapped it for a new 230v PT and it’s been fine since.
The voltage at my old house in Sydney had voltage flutuations, but it didn't flicker low, it went high to almost 250vac, I think the trick in my case would have been to use power conditioner. I probably still should have one to eliminate mains noise.
sorry for the many questions Tony 
inquisitive mind at work 
very interesting to have a bit of background and details on this.