Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: IdiotoftheYear on May 31, 2020, 03:10:59 PM
-
I have just replaced the transistors on my small Speedball board with MJE-5731A's, facing the opposite way to those provided with my kit (as instructed on page 5 of this thread https://forum.bottlehead.com/index.php?topic=5989.60 ). The voltages are now reading something like this:
OA 171V
IA 169V
IB 169V
OB 171V
No sound until I turn up the pot all the way, and even then it's extremely quiet.
How have I buggered up this time? How can I fix it?
-
Never, ever, ever, ever listen to an amp that doesn't pass its voltage checks. The voltage checks tell you it's not working. Listening to it is extremely risky to your safety and to the survival of whatever you have plugged into the Crack.
Now that I got that out of the way, why did you replace the MJE350s?
Is the 12AU7 glowing?
-
1. Replaced the MJE350s to dissipate extra heat required in order to run 12BH7 with a R1 of about 120Ohms to get an output voltage of about 70-80V. Haven't changed resistor value yet.
2. Yep 12AU7 is glowing
There's a reason why (many, actually) I'm called "idiot of the year"
-
Do you have glowing LEDs on the socket? (If not, just leave the LEDs alone for now)
Idiocy is often the most expedient avenue toward learning.
-
Yes thanks. All LEDs glowing nicely. Actually, better double check.
Edit: Confirmed - Lovely glowing action going on where it should be.
-
Could you post some photos of your build?
I just noticed that your OA and OB voltages are higher than their IA and OA counterparts. Did you remove the boards when you swapped the transistors? IA and IB go to terminals 2/4, while OA/OB go to 1 and 5. Those could well be wired in backwards. If they are not, you may have a loose black wire in the amp.
If none of that is the issue, it would be good to know that this amp did work 100% at some point.
-PB
-
My memory was wrong. Here are the correct voltage readings on the small SB board rounded to the closest integer:
OA 169V
IA 173V
B-A/B 0V
IB 173V
OB 169V
The amp was working perfectly until this morning, which is when I swapped the transistors.
-
Images
-
Can you take the mounting screws off the board, flip it up, then grab a photo of the bottom? Did you buy those transistors from a reputable seller? (eBay and AliExpress are not considered reputable)
-
Bought the transistors from a random Chinese eBay seller. Images attached. My soldering certainly won't win any beauty contests.
-
Bought the transistors from a random Chinese eBay seller.
-
;D
You can't blame a man for trying to avoid buying from Mouser, which would entail spending $24 to ship less than $4 of parts? Can you?
Actually you can. Lesson learned expediently. No trains were harmed this time, which is a blessing.
-
Hi I.O.T.Y. Are you outside of the USA? I ask because Mouser charges $7.99 shipping and I get it in : 2 days, they are in Texas and I'm in New York, That's a long haul. I love Mouser and use them almost exclusively. :)
-
Hi I.O.T.Y. Are you outside of the USA? I ask because Mouser charges $7.99 shipping and I get it in : 2 days, they are in Texas and I'm in New York, That's a long haul. I love Mouser and use them almost exclusively. :)
I come from a land down under
-
https://au.rs-online.com/web/p/bjt-bipolar-transistors/1844907/ (https://au.rs-online.com/web/p/bjt-bipolar-transistors/1844907/)
You'll have to do a side by side of the real ON vs. what you got if that ends up being the problem. To be honest the ones you have look off to me for some reason, but I don't have any ON MJE5731A here to compare to.
-
https://au.rs-online.com/web/p/bjt-bipolar-transistors/1844907/ (https://au.rs-online.com/web/p/bjt-bipolar-transistors/1844907/)
You'll have to do a side by side of the real ON vs. what you got if that ends up being the problem. To be honest the ones you have look off to me for some reason, but I don't have any ON MJE5731A here to compare to.
Marvellous! Thank you sir.
-
Cheers Mate, I had vegemite on toast this morning, I'm serious
-
Cheers Mate, I had vegemite on toast this morning, I'm serious
You had Vegemite on toast? And I thought that I was an idiot! ;)
Actually, we eat Vegemite regularly. One of my favourite home-cooked meals involves minced meat and onions rolled in pastry and basted with a blend of Vegemite and hot water. A fourth generation family recipe and a tasty one at that. Thanks great grandma! An Australian national hero.
-
That sounds good, if I understand cook mince and onions, drain wrap in pastry and bake basting with the veg and water from time to time when baking? or after baking? I may try this. I've made beef pasties in the past and have used vegemite in baking such as cheese cake and chocolate ganache. It may sound weird but maybe I am an idiot. And may I be so bold to ask about the ratio of vegemite and water? I understand that you may have trepidation divulging your great grandmothers secret family recipe but it sounds intriguing to me. I promise I won't tell anyone. What was the original topic I forgot. ;D
-
Here you are Lee:
Meat Rolly Polly
2 x Cups of SR flour
1 tablespoon butter
Pinch of salt & pepper
Milk
500 gm minced beef
1 onion, chopped
Beef stock cube
1 cup of boiling water
A couple of teaspoons of Vegemite
Mix self-raising flour, butter, salt & pepper and enough milk to make a firm dough. Roll into a rectangle. Place mince, onion and the beef stock cube (dissolved into boiling water) into a bowl and mix. Spread onto dough, roll up and stick ends shut. Chop into snail-like pieces and place flat into a baking dish.
Baste Mixture: Mix Vegemite, butter and boiling water and pour over snails. Cook in the oven for 20 mins at 200 degrees Celcius. Reduce heat to 180 degrees and cook for 45-60 minutes. Baste with liquid when necessary.
You might find that you need to make more of the basting mixture. You don't want the pastry to get too dry during the cooking.
Vegemite in cheese cake and chocolate ganache sounds.... interesting. Might have to try it some time.
https://youtu.be/B4Asqq78nBE
-
Thank you sir I will give it a try before the weather gets to hot to run the oven, we will be getting miserably hot and humid weather soon. enjoy the hobby and I promise no more hijacks of your thread. I think, maybe, I'm not sure...…. :-\
-
Hopefully you don't get your Vegemite from the same eBay seller who sold you those transistors.
-
Got 'em!