that means you have about 47mA running through the resistor. without further measurement we can assume maybe 5% of that current is grid bias current.... so 95% of 47mA is 45mA. now the plate voltage on the valve is 435 volts.
multiplying them together will give the IDLE dissipation. so 435 x .045=19.75 watts. this is about 66% of the maximum plate dissipation (30w)... a little hot.  60% seems to be the industry standard.

now remember, more power will be put through the tubes when you play, so i would say this is a little on the hot side. most people will bias at approx 60% which gives a good compromise between tone and tube life time.

according to nik, his optimal bias point is 37 mA which is on the cool side. (i remember reading somewhere that dumbles should be biased cool) 40 mA would be a good compromise (which is about 60%) and 43 would be considered "hot"

hope this helps.

the gnx is a very good preamp and therefore has lots of gain. its able to drive a valve amp hard, in fact its capable of driving a power amp on its own. because of this if the level from the output of the gnx is too high the klein does not seem to like it, probably because its designed to accept lower levels at the levels of guitars and normal effect pedals.

to get a good acceptable level out of the GNX ot any multieffector. plug it into your amp and and run it bypassed and then unbypassed, and adjust the output level to match. as i said, i little higher level is ok, but too much seems to drive the klein into levels it was never designed to operate at.

hope this is clear

according to nik 5mv difference or so is acceptable. 10mV is a bit on the high side (hence my balance pot mod)
did you buy them as a matched pair?

mr apologies everyone. my mistake. i read my schematic after i modified for valve transconductance mismatch. i have found that sometime valves will drift in transconductance with time and hence placed a balancing pot in there, mistaking it for niks original design.

the bias pot on the HRM is set in a complementary fashion. so if you incease the current to one tube, the other will decrease. nik obviously made it this way so there is little chance to setting too high current.

the phase inverter is AC coupled to the output stage and therefore has no influence in the quiescent setting on the amp.
as i said, you cannot change the overall current for the output tubes because as you increase the current on one, the other will be opposite. using this design, you will find a nominal pont where the quiescenet current through the two tubes are equal. the voltage measurements across the 1 ohm resistors are there to give you the current measurements  for each tube so that you can balance the current between the two tubes and also ensure that the power specs for the tube are not exceeded

i suggest you look at the schematic and see how its done

i had jj's before. but i never liked them for their tone... too bassy and midrange to me. i tried EH and Mullar preamp tubes in the preamp and ended up using the Mullards because them were a little more gainy than EH. but EH are good too.

i spoke with tube wholesaler i know, who could sell me any brand i wanted, and told me that whilst the EH are good, the WINGED C were ther best at the moment. he suggested i try them or else he would exchange them.

well i am very happy, especially after burning them in

Dear dennis
i am an electronics engineer, and know my stuff believe me. the current on the valves is more or less set to the nominal value. the bias pot is there to compensate for any differences in transdconductance between the two tubes, allowing them to be symmentrical.

the g12-65 is a nice speaker at  low and moderate volumes however you just lose the sparkle at higher volumes. hence peoples preference for the EVM-12l.  as i turn my g1265 up it colors the sound too much and becomes muddy. so i plan to use the g12-65 in a second cab for gigs  to give me extra oomph. ... and i am putting an evm 12l in the combo for everything else. i believe the evm will not change its characteristics too much as its turned up.

once it arrives and i have it fitted i will post my opinions .

when i first got my amp, i used my GNX4 in the effects loop with the klein. if the output level on the gnx was too high the amp would howl terribly especially with the 3 klein knobs set to 50%. i found that setting a level comparable (or maybe a little louder) than your guitar level on the gnx was optimal, especially in getting extra sparkle in the tone.

nowadays i use a reverb and delay pedals in the loop and they work just fine.

hope this helps.

the components which are most affected through the burn in period are the Tubes (valves) and the speaker(s). these components will change their intrinsic characteristics after being "burned in" and settle.

if old fashion cabon composite resistors are used , then these will definitely drift as well throughout the lifetime of the amp.

its definitely recommended to burn in new valves after changing them, do you dont get any nasty surprises when you want the amp to be at its best behavior during gigs or rehearsals.

capacitors will change, however this will be longer term thing with the ageing process as the electrolyte in them dries out, however have negligible drift during the burn period of a few weeks or months.

if you look under the chaasis, between to the output tubes you will see a pot with no knob on it. in the first picture you posted you will see two red banana connectors (well the back of them).... and one black one.

to check your bias, you dont need to remove the chassis. you simply use a DVM able to read mV and measure between red and black for each valve. you need to get the voltages as close to identical as practicable. the bia pot will allow you to do this. make sure your tubes have been on for at least 5 to 10 minutes and all master volumes turned to 0.

try to buy matched sets. the reason being is that the bias current is set on the amp, and therefore the bias to balance the valves will be minimal.


hope this helps.

a week ago i upgraded the output tubes to  Winged C (SED) 6l6gc. i had read reviews stating they were very close to the RCA's of old. well i must say, my initial impressions was the amp was suddenly 3D!!. these tubes were made for this amp. i suggest anyone looking to upgrade their output tubes to go for these. even at higher volumes, they are excellent.

hi nano
i have a 70's vox ac30tb with fanes and i must say, its a great amp especially when turned up, as the fanes do not break up as much as celestions. so you get to keep your trebles more at higher volumes.

my HRM has a G12-65 which is good at lower volumes but fattens up and loses trebles (ie clarity) at higher volumes. i have just purchased a EVM12L to go into my combo, and move the G12-65 into a 112 box (open back) so i can get a good blend of the two.

weber make clones of the Fane AXA12 and the JBL. i have used webers before and they make excellent speakers and are very good quality-wise too. albeit the webers i have are alnico blues, they are faithful reproductions of the originals... so i would not hesitate in recommending the others either. these guys know their speakers.

i almost went for the delta as well but could not find a 16 ohm one....(just as well heh!!)

i have always been a fan of mixing speakers.... with careful selection, you can reaaly get a good coverage of the entire spectrum and produce some wonderful tones.

i hear the JBL E120 is another speaker in the same hertitage abd characteristics as the EV. also a favorite for people who want to maintain their tone at all volumes.

strangely... both speakers were used by fender in the 70's for the twins, which were notorious for very loud piercing volume and very little coloration.. and this was the era when twins were at their worst!!!

another speaker from that period was a brand called "Gauss" which i dont hear much about these days, but i believe they were similar to EV and JBL's

Hi Dr Ika
given you have used Fanes, Celestions and now EV speakers with your OTS,
which is your favorite?

would you use the EV in an open cab?