Correct, Ik=62ma.
What's your estimated output power? (see the table at the bottom of this page):
Tubes & Transformers
Load Z is your output transformer primary impedance.
Last edited:
Nice! It sings! The RCA jacks and speaker jacks in cardboard boxes are a nice touch.
Looks like you've got a motor run cap as well.
Now you need a chassis. You can use a baking pan upside down for a quick and dirty chassis, you just need a unibit to drill the tube holes.
The voltage across C2 is your B+ voltage. If you jumper or install a switch across SW1-SW1 you be using SS rectification and your B+ will increase a little.
What is the primary impedance of your output transformers?
Looks like you've got a motor run cap as well.
Now you need a chassis. You can use a baking pan upside down for a quick and dirty chassis, you just need a unibit to drill the tube holes.
The voltage across C2 is your B+ voltage. If you jumper or install a switch across SW1-SW1 you be using SS rectification and your B+ will increase a little.
What is the primary impedance of your output transformers?
Last edited:
I am working on an aluminum chassis now . Thinking of adding some wood for the faces of the chassis . Dont know yet ....
Anyway, I added the run cap and it removed most of the hum I had before .
I have a problem with my POT , anyone can
Offer such POT from mouser/farnell?
In case I would like to increase the maximum volume I have now (max output power), the right approach is by changing tubes?
Anyway, I added the run cap and it removed most of the hum I had before .
I have a problem with my POT , anyone can
Offer such POT from mouser/farnell?
In case I would like to increase the maximum volume I have now (max output power), the right approach is by changing tubes?
What's the problem with the pot? A cost effective upgrade alternative is a stepped attenuator off of ebay from China.
You can increase the power out by increasing the B+ and bias current (by reducing the value of R17 & R27) as long as you do not exceed the max power dissipation specs of whatever tubes that you are using. Tubelab's tables are your friend here.
One note on the tables; IIRC, the tables are for triode wired outputs. If you are using UL, your output will be higher.
In Tubelab's tables, notice the values in red, these are busting out of the published max power spec of the output tubes. You can usually exceed the max dissipation values a little without much trouble, although that depends on the tubes. Also, the harder you crank the B+ and bias current, the shorter the tube life will be. On average you can expect 2000-3000 hours out of your tubes (big generalization here...).
Again, looking at the tables, the max power out will be with KT88's. They can handle higher B+ and bias current without busting the max power dissipation spec.
You can easily raise your B+ just by jumpering SW1-SW1, that will give you SS rectification (the rectifier tube will just sit there and do nothing or you can remove it). It will probably go up about 30V or so, since the diodes drop about 1.4V and the rectifier drops about 30 volts or so. SS rectification gives you a lower PS output impedance, a good thing (your motor run cap lowers the output impedance as well).
The easy way to get more output is to use high sensivity speakers, like 93-95db 1W/1M. These amps really shine with high sensitivity full range speakers. Small two way bookshelf speaks are generally fairly inefficient, like 86-87db.
Are you including the switches for UL/triode and SS/tube rectification?
You could also do a cathode R selector with multiple resistors of you want to run different output tubes.
Rknize has a great example of this; it's posted in a few threads around here.
The combo of SS/tube rectification and cathode R switch gives 2 B+ voltages and a range of bias currents.
You may want to consider putting these around the back or some other non-obvious place to minimize the possibility of these getting flipped with the amp powered up.
Methodically.....
First off, you know it worked once not too long ago....
So you have that going for you.
.......and you know it's not the PS as one channel is working.
Triple check your wiring, then check it again.
Are all the filaments lit? Dim the room lights to check if req'd.
I would suggest checking the DC voltages at the pins of the both the 12AT7 and the output tube of the dead channel to start with. Do so carefully with one hand or clip leads, as a few pins will have high voltage on them. You can also compare the various pin voltages from the working channel to the dead channel.
Let us know what you find out.
First off, you know it worked once not too long ago....
So you have that going for you........and you know it's not the PS as one channel is working.
Triple check your wiring, then check it again.
Are all the filaments lit? Dim the room lights to check if req'd.
I would suggest checking the DC voltages at the pins of the both the 12AT7 and the output tube of the dead channel to start with. Do so carefully with one hand or clip leads, as a few pins will have high voltage on them. You can also compare the various pin voltages from the working channel to the dead channel.
Let us know what you find out.
Well I found the problem (something I was suspected in) - the POT. this one was with PCB legs so there is a problem to solder wiring to it (especially thin ones). I bypassed the POT and both channels are working.
Now I am waiting for another POT, can you say whether this one is a suitable one ?
RV24BF-10-15R1-A50K Alpha (Taiwan) | Mouser
Now I am waiting for another POT, can you say whether this one is a suitable one ?
RV24BF-10-15R1-A50K Alpha (Taiwan) | Mouser
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.