6x 6550/kt88 bass amp build

[ThermionicScott]

That's a beast! How much does it weigh?

- Scott

[Steve Conner]

Yeah, how about an update on this project black_labb! We're all eager to see some koala bears shaken out of their trees at 100 paces.

[Vortexion]

Been reading this with fascination, black labb. Fantastic stuff: a beast indeed - I'm glad I don't have to lift it!

I like your use of hefty aluminium extrusions for the chassis sections: instant strength and rigidity, plus you neatly avoid any of the inductive issues associated with steel. Nice.

I do have m'worries, though, re. heat and ventilation - i.e. that there'll be too much of the first going on and not enough of the second.

Looking at your pics, these are the issues I'm seeing. Purely IMHO stuff, of course, but I feel they're worth mentioning...


Proximity of components:

The two B9A valves on the main chassis, next to the toroids: they're really far too close to that 6550. When this baby gets going at full power, they're just going to cook, mate.

Likewise, the two B9A valves that sit horizontally back from the pre-amp chassis: the top of each one is extremely close to the side of a 6550. Fortunately, they could be re-positioned quite easily.

The rearmost toroid is, by the look of it, only about 11/2 inches away from the rear left 6550. That's too close, IMO. In time, it will suffer from heat -related issues.

Ventilation:

You've got some decent-sized holes in the front and back of the case, but I'm not at all sure that the two small fans in the roof can really provide enough airflow (or - just as important - an even pattern of airflow) to properly cool 6x6550s.

Fortunately, nature has provided us with the perfect solution: hot air rises! If given enough opportunity for vertical convection, those big bottles will cool themselves very well without any need for fans. If I were in your shoes, I'd take advantage of that thick, rigid aluminium chassis to do the following:

1) Cut a great big rectangular hole in the bottom of the wooden case (and I mean BIG: large enough to encompass the whole area taken up by the power valve sockets) and cover it with a rigid metal grille.

2) If it isn't so already, mount the case on tall rubber feet - at least an inch high.

3) Drill numerous holes in the top surface of the power amp chassis, between and around the 6550 sockets. In other words, turn that solid block of Ali into a swiss cheese!

4) Cut another great big hole in the roof of the case and cover it with a rigid metal grille.

Job done!

OK, I know that now you've got all the components in there, step (3) will be a swine to do - and yes, step (4) will definitely lay the amp open to spilled liquids (answer: NEVER PUT YER TINNY ON TOP OF THE AMP! ), but I promise you that it will provide those hot bottles with the best cooling possible, and you'll have no worries about failing or noisy fans. This is what I did to my Trace Elliot VA350 and It runs very happily with no overheating issues.

ADDED LATER:
Morgan Jones has a nifty way of doing step (3). Y'know the circular metal guards that are made for fans? Cut out the centre part of the guard and mount your octal socket in the hole. Then cut a large diameter hole in the chassis for each 6550 and mount a fan grille over each hole. Result: perfect chimney cooling per valve! Picture:

[black_labb]

That's a beast! How much does it weigh?

- Scott

just weighed it now. comes to 30kg (66 lbs). not too bad considering. guess the torroids were helpful in keeping the weight down.

Yeah, how about an update on this project black_labb! We're all eager to see some koala bears shaken out of their trees at 100 paces.

well it hasnt changed much really. been busy at work (i work casual at a small butchershop, and there is alot of work to be done for christmas hams)
got the fans in, they are currently running off a 16v supply with the 2 fans in series (8v each). there is still a fair bit of flow at 8v as the fans are high output fans for their size, and they are pretty quiet.
i realised that when i thought the fan supply was blowing fuses was because i was using a small fuse on the mains and forgot that the plate supply charges up pretty quickly through 750ohms when on standby which was blowing the small fuse. forgot about the standby that charges up the big caps.

Been reading this with fascination, black labb. Fantastic stuff: a beast indeed - I'm glad I don't have to lift it!

I like your use of hefty aluminium extrusions for the chassis sections: instant strength and rigidity, plus you neatly avoid any of the inductive issues associated with steel. Nice.

I do have m'worries, though, re. heat and ventilation - i.e. that there'll be too much of the first going on and not enough of the second.

Looking at your pics, these are the issues I'm seeing. Purely IMHO stuff, of course, but I feel they're worth mentioning...


Proximity of components:

The two B9A valves on the main chassis, next to the toroids: they're really far too close to that 6550. When this baby gets going at full power, they're just going to cook, mate.

Likewise, the two B9A valves that sit horizontally back from the pre-amp chassis: the top of each one is extremely close to the side of a 6550. Fortunately, they could be re-positioned quite easily.

The rearmost toroid is, by the look of it, only about 11/2 inches away from the rear left 6550. That's too close, IMO. In time, it will suffer from heat -related issues.

Ventilation:

You've got some decent-sized holes in the front and back of the case, but I'm not at all sure that the two small fans in the roof can really provide enough airflow (or - just as important - an even pattern of airflow) to properly cool 6x6550s.

Fortunately, nature has provided us with the perfect solution: hot air rises! If given enough opportunity for vertical convection, those big bottles will cool themselves very well without any need for fans. If I were in your shoes, I'd take advantage of that thick, rigid aluminium chassis to do the following:

1) Cut a great big rectangular hole in the bottom of the wooden case (and I mean BIG: large enough to encompass the whole area taken up by the power valve sockets) and cover it with a rigid metal grille.

2) If it isn't so already, mount the case on tall rubber feet - at least an inch high.

3) Drill numerous holes in the top surface of the power amp chassis, between and around the 6550 sockets. In other words, turn that solid block of Ali into a swiss cheese!

4) Cut another great big hole in the roof of the case and cover it with a rigid metal grille.

Job done!

OK, I know that now you've got all the components in there, step (3) will be a swine to do - and yes, step (4) will definitely lay the amp open to spilled liquids (answer: NEVER PUT YER TINNY ON TOP OF THE AMP! ), but I promise you that it will provide those hot bottles with the best cooling possible, and you'll have no worries about failing or noisy fans. This is what I did to my Trace Elliot VA350 and It runs very happily with no overheating issues.

ADDED LATER:
Morgan Jones has a nifty way of doing step (3). Y'know the circular metal guards that are made for fans? Cut out the centre part of the guard and mount your octal socket in the hole. Then cut a large diameter hole in the chassis for each 6550 and mount a fan grille over each hole. Result: perfect chimney cooling per valve! Picture:

thanks vortexion
i have been considering remounting the preamp chassis to fit along the top of the box, and making a bigger cutout to the front and maybe mount the fans there to have a more direct flow out of the box. would also mean i wouldn't have the useless control/light to figure out as i would be able to redo the holes. i think it would look better with big vents like the back on the front anyway.

the ideas are good ways to get the heat circulating, but i dont think they will be neccesary. i'd rather rearrange the preamp and fans as mentioned above first. the way the componenents are mounted in the amp makes it difficult to do, and it doesnt look very professional. i do like the fan cover idea though. wouldnt work with the tagboards i have mounted, but a good idea for future designs. dont know if i would need another amp of this magnitude anytime soon though.

i'll give it a good workout when i have some time and put a thermometer in there to see what kind of temps things get at.

[Vortexion]

Best of luck, mate - keep us posted!

[MarcoMike]

hey! great work (huge work, actually...) how much is the weight in the end?!

for a clipping "meter" I can suggest you to take a look at the ampeg svt3 schematic... there's a very simple solution, but I guess you need to calibrate it to the actual clipping treshold of your amp...

oh, by the way, this is my first post here, so... Hello everyone!!

EDIT: I've just seen other posts I didn't notice... probably I still have to learn how this forum works...

[black_labb]

thanks marcomike.
the weight came to 30kg/66lbs
thanks for the tip for the clipping meter.

[Kagliostro]

Very nice job!

can you post a schematic

Thanks

Kagliostro