ac30 layout

[kwm488]

hi

i think my ac30 white noise is normal. but if someone can prove it. it will more perfect for me.

i try to use the PT heater CT , so i don't ground one side heater. but i don't think the noise level different. both are same.

sorry, this is my first EL84 amp. i have some question. do anyone can help me

1. can i use two EL84 for this amp like fender marshall? i just try it with 2 EL84. but that two EL84 super super hot even my amp just turn on few minutes.

2. can i add 1ohm resistor for EL84 tube socket like marshall fender amp. so i can know the tube bias.

3. the brilliance channel have white noise when i turn the amp about 2:00. and if i adjust the bass and treble , noise level will different. honestly, i think this should be normal. but i really hope someone who own vintage ac30 amp can prove it for me
thanks

[sluckey]

1. can i use two EL84 for this amp like fender marshall? i just try it with 2 EL84. but that two EL84 super super hot even my amp just turn on few minutes.

Yes. But since it's cathode biased you will need to change the cathode resistor to 130Ω when you pull two tubes.

2. can i add 1ohm resistor for EL84 tube socket like marshall fender amp. so i can know the tube bias.

Yes. See page 2 of the following pdf for an example...

     http://home.comcast.net/~seluckey/amps/VAC15/Vox_AC15.pdf

3. the brilliance channel have white noise when i turn the amp about 2:00. and if i adjust the bass and treble , noise level will different. honestly, i think this should be normal. but i really hope someone who own vintage ac30 amp can prove it for me

I think it's normal but I can't prove it.

[kwm488]

thank you.

sorry for once more question.

i used two el84 for few minute without change the cathode resistor to 130ohm. will that two EL84 dead or hurt?
that two tube very hot. and have little smell. i stop immediately.

btw, that is mullard

[sluckey]

They were definitely stressed. I would not think they are dead. Hard to say if they were harmed, but probably not. Did they redplate?

[kwm488]

Hi

No red plate. But the tube is very hot.
So isl it hurt?

[sluckey]

They were definitely stressed. I would not think they are dead. Hard to say if they were harmed, but probably not. Did they redplate?

[kwm488]

No redplate

[kwm488]

the cab is arrive today. i wait it 2 months. it is very very nice.







and i need help. i confirm my amp have noise problem. it is not normal. when i turn on the amp. all volume to zero. but my amp have little 60hz hum. do anyone can teach me where can i start to fix it?

please help

[kwm488]

hi

i do a lot of test and research , i think the brilliant channel hum is normal.

but i have big problem now, the EL84 tube are super hot. and i do research, some user point this out too.
my vox ac30 PT can switch to 240v (here is 220v). will this help to lower the B+. or i need to change the 47R bias resistor to 68R or 82R?

[sluckey]

my vox ac30 PT can switch to 240v (here is 220v). will this help to lower the B+.

It should. Flip the switch and see if it's enough reduction.

or i need to change the 47R bias resistor to 68R or 82R?

That's an option too. It won't lower the B+ but it will allow the tubes to run cooler.

[kwm488]

Hi
Btw, i really don't know how the people use ac30 in the past.
I install new gold lion el84 today. I used the amp 2 hrs. The tube is dead.

[kagliostro]

Try with 6p14p-EV or 6p14p-K


http://www.tubes.ru/techinfo/HiFiAudio/6p14pev.html



they are a strongher version of el84 tubes


K

[kwm488]

hi

i measure the voltage today. the EL84 plate is 339v. and the bias is 10.64v.

but i find out the one important thing. the 47R bias resistor. it is very hot even i turn on the amp 1 and 2 minutes. i used 10w resistor here. i measure the ohm. it is increase to 89R when this resistor is hot. i believe this resistor will over heat if i turn on the amp about 1 or 2 hrs.
now, i changed it to 20w resistor.

will my new EL84 tube dead (red plate) very fast because of this bias resistor?
thanks

[kagliostro]

47R was a very early value, it will be better if you swap to 68R or 82R


K

[kwm488]

Hi
I used 220v tap before. Heater is 6.6v.

I use 240v tap now.
heater is 6.1v
plate 309v
bias 9.35v

I may change to 230v.

Btw, some people say 82ohm is early version. And i will use 230 or 240 tap. Should i still need to change 47r to 82r bias resistor?

[sluckey]

10.64v across a 47Ω resistor will dissipate 2.4 watts. You're 10 watt resistor will be fine. They are supposed to get hot. Just give it plenty of air circulation around it, ie, don't mount it flat on a pcb.

[kagliostro]

You are right about the value of the resistor the oldest schematic I've seen (1960) say 50R the 47R version was on a 1978 amp


---



on the CC2 there are two resistors one is 82R and is paralleled with a 150R via the HOT/WARM switch


82R is considered Warm - 50R (82R || 150R) is considered Hot


on the CC2 the bias voltage is 11v with 50R and 13v with 82R -- B+ on CC2 vary from 321v to 324v


K

[kwm488]

Hi
I think i will use 230v tap.
 may increase bias don't need to use match el84? Whatbenefits if i use separate bias resistor for each tubenefits if i use seperateistor value.

I see weber ac30 schematic. Plate voltage is 320v.

And vintage ac30 schematic, plate voltage is 320v too(but it mark down it is measure by vintage multimeter, modern multmeter should 5% higher)


But the main problem i have, the 10w bias resistor super hot when i run the amp few minutes. I guess this resistor lost the function when super heat. So it kill my el84. Ac30 Layout request me to use 12w resistor here, but i use 10w. 10w not enough?

Last, i am newbie of ac30 style bias. Is it mean i dont need to use match el84? What benefits if i use separate biss resistor for each tube?

[sluckey]

But the main problem i have, the 10w bias resistor super hot when i run the amp few minutes. I guess this resistor lost the function when super heat. So it kill my el84. Ac30 Layout request me to use 12w resistor here, but i use 10w. 10w not enough?

10.64v across a 47Ω resistor will dissipate 2.4 watts. You're 10 watt resistor will be fine.

Pay attention!

[kwm488]

But the main problem i have, the 10w bias resistor super hot when i run the amp few minutes. I guess this resistor lost the function when super heat. So it kill my el84. Ac30 Layout request me to use 12w resistor here, but i use 10w. 10w not enough?

10.64v across a 47Ω resistor will dissipate 2.4 watts. You're 10 watt resistor will be fine.

Pay attention!

I am confuse, if 2.4w dissipate only. When that resistor will very hot. I can't use my hand to touch it. Is something wrong?

[sluckey]

I am confuse, if 2.4w dissipate only. When that resistor will very hot. I can't use my hand to touch it. Is something wrong?

I used your numbers. But a 10 watt resistor that's dissipating 2.4 watts will put a blister on you finger,

[kwm488]

Is "will put a blister on you finger" mean this resistor should very hot, it is normal? i apologize for my bad english

Btw, i suspect the 250uf 25v (tested is 325uf, it is normal for vintage erie caps) capacitor have problem, maybe leak. (It parallel with bias resistor)But my friend tell me will not. If leak, the resistor should not heat. Current will flow to cap mainly.

[sluckey]

Is "will put a blister on you finger" mean this resistor should very hot, it is normal? i apologize for my bad english

I understand your English. Do you understand mine?

[kwm488]

I understand now. I asked my friend.

So 10w resistor dissipate 2.4w, it will very hot normally.
Just dissipate 2.4w, so it will very hot?
Anyways, i try 20w resistor now.

[kwm488]

HI
i spent whole day to fix my ac30 today.

i did follow

1. add shield cable to PI tube grid pin.
2. try another wire for cut control.
3. changed PI capacitor
4. changed 47ohm bias resistor to 100ohm
5. add shield wire for brilliant pot to top boost tube pin2
6. try to increase main filter cap from 16+16uf to 32+32uf
7. try to change all filter cap.

but all don't help. how should i do ?

i just want to fix (if i turn the brilliant vol pot over 2:00 or 3:00, will have hum). i think it is 50hz hum.

i try to pull PI tube. so it is no hum even i turn brilliant vol pot to max. and i pull top boost tube. it is also no hum even i turn brilliant vol pot to max. when i try to pull other preamp tube. all have hum .