BHK250 Tubes

Has any one had trouble changing the tubes on there amp , today I spent 15 mins taking the tubes out they were a very tight fit and then another 20 mins putting in the new ones , it was much harder putting them back in . I had to replace one as it was buzzing on the right speaker . Not a simple job as one would expect had to take amp out of the hifi table set it on its side so that I could get a firm grip on the tube to slowly pull out slightly pulling side to side must have sweated a pint of fluid (its hot here in Perth , Australia ) don’t want to be doing this to many times my hands feel like I had been on the punching bag for a hour .

It can be difficult depending on the grip of the socket. But I have done it several times with ease, and a few others with trouble. It’s always a challenge as a manufacturer to keep the socket’s grip firm and the ease of taking the tubes in and out easy. I am glad you were able to get it done.

…and a new line of home exercise equipment is born!4_gif

A “toight” tube socket is a beautiful thing. A little circular motion helps quite a bit.

I was lucky enough to be a beta tester for the BHK 250 and we were shipped a kit to fix the tight sockets by using a pin to expand each one. Don’t know if you got one of the ‘fixed’ ones or not. But I did do the procedure and the new tubes went in fine.


SSW, you got a kit to expand tube sockets? I was a Beta tester too and didn’t get one. Haven’t had a need to remove tubes … yet.

Yup, it was a simple thing to do to remove the (tight) tube and use the tool in each socket contact to expand the sockets one at a time. They may have done this at the factory before you got yours. But they were really tight.


It was just a rod that came in the box with the spare tubes. You may have missed it Peter. Or maybe it got left out.

I do not have it either. Do you have a photo?

Steve, “spare tubes”? I only got one set, is that what everyone else got? If it was just a rod (makes sense) I could very well have missed it. If anyone recalls where it was stored perhaps that will help me find it! I may play with tube rolling in the next few months if I get bored (I’m not much of a tweaker). Having owned a few tube based components I know what it’s like to have a stubborn tube.

By the way, I should add that my BHK 250 has been operating flawlessly ever since I got it. Very happy with my purchase as I am sure many others are!

It may have only gone with the first units and may well have been shipped afterwards; my memory is failing but that is very possible. It looks like a small white candle (i.e., the handle) with a short thin rod sticking out. It also came with a pair of white gloves, all in a small white box. I wouldn’t worry about it. You should get the same result just pulling and reinserting the tubes a couple times.

Right. We only had the tough sockets in the very first units and we made a little tool that could be used to open them up a bit - very few needed that tool. The tool is really nothing more than a small metal ‘poker’ that opened up the sockets a little wider to make it easier to insert the tube.

A delightfully quirky bit of BHK250 history.

Having owned and own a good number of products with tubes (16 glowing away right now) I have found a good deal of variation in sockets, as with any mechanical thing. As already mentioned, gentle rocking helps a great deal - but never twist.

Tubes themselves are very sturdy (hold them by the base when inserting and removing). Audiophiles love to fuss over them as fragile holy objects, but they were/are designed to handle a good deal of abuse and rough handling. The venerated 300B was originally produced in 1938 to amplify telephone signals, with a life expectancy of 40,000 hours, and is so tough it was used used submerged in the in the Bell Systems transatlantic cable amps.

No one wore white gloves or obsessed over replacing a tube in a 1950’s television. A quick trip to the hardware store, pull out the old and and push in the tube.

I was busy last night packing my spousal unit up to get her to TeslaCon, so when I get a chance I’ll take a picture and get the diameter of the pin so you guys can make your own tool with a drill bit. (Don’t use the pointy end)


Elk said No one wore white gloves or obsessed over replacing a tube in a 1950's television. A quick trip to the hardware store, pull out the old and and push in the tube.
I remember my father pulling tubes out of our old black & white set and taking them to the super market/variety store, which had a tube tester and sold tubes, of course. People didn't replace tubes in those days until they failed (high-end audio may have been different even then but we did not have a family stereo of any kind when I was a kid).

Steve/Paul, your comment about early units would explain it. I have one of the last Beta units so it must have been “fixed” by then. No big deal, just got my attention!

As for memories of tubes, I loved to “diagnose” our tube TV by taking them out and going to the local Lafayette Radio store where you could test to your hearts content. Such fun for a kid, too bad I never really took the fascination with tubes into building my own. Oh, opportunity lost…

And think of all the tube testers which were simply tossed as transistors took over.

All those testers ‘Down the tubes’. 4_gif


Elk said And think of all the tube testers which were simply tossed as transistors took over.
Yup, so sad ... But a few of them are collectible and worth quite a bit, mostly Hickoks. And to think of all the tubes that were tossed too, though many were of no use for audio.

J.P.- Good one!

Pin is 1.18 mm diameter, or 0.46"

#56 drill



Just want to say that today, my system hit different. Thanks to new NOS Mullard ECC88s :smiley: