Heath SB 220 suicide intervention.

[nomadradio]

The SB-220 that gets the first pair of our substitute meters had another issue that seems worth mentioning, at least briefly.

This fan may have moved more air, but it's completely, suicidally wrong.

May not be obvious from the outside, but this view reveals that ALL the air is now directed at the tubes above the deck. No airflow reaches the undersides of the tube sockets.

Bad idea. Eimac says you need at least a gentle breeze across the tube's pins and the spring contacts UNDER the socket. This fan won't do that, no matter how hard it blows.

Here is the factory type fan, along with a new perforated mounting plate I robbed from a junker.

Doesn't look much different from above.

But from below, you can see how the blades blow across the underside of the chassis onto the sockets.

But now I need to start a new thread about the meters. This one has gotten long enough.

But it seemed worth pointing out. Heathkit deliberately chose a fan design that would be surprisingly quiet. It moves no more air than you need to run it like they recommend. That's the sacrifice they made to keep down the fan noise.

But a fan with more output is only useful if it also blows across the undersides of the sockets as well.

The one they put into this amplifier would not. Fortunately it came to us before the sockets were ruined.
73

 

[BJ radionut]

https://harbachelectronics.com/shop/heathkit-sb220-sb221/fm-220-replacement-fan-motor/
I am sure you have seen these, Nomad.
I have used maybe 4 of these so far, work very well and slightly more volume than originals...As 3-500's are notorious for melting solder out of the pins of the tube base, plus wasting sockets without proper cooling.
All the Best
Gary

 

[wavrider]

I 2nd what Gary posted.
I have one big honking soldering iron to reflow/add solder to the filaments of the 3-500Z due to being over heated and melting the solder at the pins.

I use hardbach replacement fans for upgrade and have no issues with them at all.

Now on the JB2000 type amplifiers that is another issue all together.
small 12vdc computer fans work great installed under the chassis.

 

[Onelasttime]

Yes for some reason people do not seem to understand that the pins need cooling too! Seems like common sense to me but my wife often reminds me that common sense is anything but common. Men today seem to have no understanding at all in mass of how things work! Hell you cannot find a man that knows how to jump start a car or drive a manual transmission that is under 45 years old in America. Do not even think about how a carburetor works or how to read spark plugs! Understanding a vacuum tube might as well be advanced mathematics or the like! How do you think so many fall victim to the stupid garbage sold on late night TV!!!!

 

[nomadradio]

It's also no accident that the tube's two cathode pins are usually the first ones to melt.

They carry about 15 Amps of filament current. Even when everything is perfect, you have heat that's conducted out of the hot filament, down the pin and into the socket.

Any oxidation or schmoo on the surface of the pins, or on the surface of the socket's spring contacts will cause a small voltage drop. The heat from this just adds to the other sources heating the filament pins.

When the socket temperature rises to an unsafe level, the three grid pins will always be a few degrees cooler than the two filament pins. If you see visible signs of melted solder on all five pins, a tube was run REALLY hot to do that.

But if you see signs of melted solder only on the two filament pins, the tube is still cooked, but maybe only half-cooked.

73

 

[543_Dallas]

Heapshit should have took some notes from drake when they designed these things. They took 2 good tubes, stole a fan from a sweep tube leenyar and topped it off with an anemic power supply. I've saw people ask Henry prices for these things.

 

[Shadetree Mechanic]

I wonder if a heat sink could be made for the pins? Maybe use brass tube to extend them so they stick out of the back of the socket and catch some air?

 

[Staybolt]

Yes for some reason people do not seem to understand that the pins need cooling too! Seems like common sense to me but my wife often reminds me that common sense is anything but common. Men today seem to have no understanding at all in mass of how things work! Hell you cannot find a man that knows how to jump start a car or drive a manual transmission that is under 45 years old in America. Do not even think about how a carburetor works or how to read spark plugs! Understanding a vacuum tube might as well be advanced mathematics or the like! How do you think so many fall victim to the stupid garbage sold on late night TV!!!!

Really. Im 44 years old and first car i ever drove was a stick and iv'e replaced spark plugs and done my own tune ups....... So you're wrong here.

 

[543_Dallas]

Really. Im 44 years old and first car i ever drove was a stick and iv'e replaced spark plugs and done my own tune ups....... So you're wrong here.

I made it to 30 before I bought my first vehicle with an automatic transmission. That was only about 6 months ago. I went from an old ford with a 4 speed in high school to a dodge with a 6 speed manual that I put over 300k on. I still drive the old diesel a couple of times a month, I honestly like it more than the new one.