How much room to leave for tubes in amp head?

[joulupukki]

I made some nice 1x12 speaker cabs and an amp head for an upcoming 18w TMB project and have enough lumber and tolex left to make another small head. I'm thinking I'll build a RobRobinette.com's Bassman Micro head (https://robrobinette.com/Bassman_Micro.htm).

I'm going to build the head cabinet just wide enough for one of the Hammond chassis boxes but how much room should I leave from the top of the chassis to the top of the cabinet? From what I gather, the rectifier tube and power transformer will probably stick up the highest, just under 3". Should I go for about 5" clearance between the chassis top to the underside of the top of the cab?

Here's how my other cabs turned out. I'll probably build the micro head in a similar style though I'm not sure if I'll do the welting on the top or not. I'll use probably just a simple black leather style handle instead of the Marshall-style handles.

 

[corliss1]

Typically the answer is "enough to get the tubes out without needing to pull the chassis" - there's no official rules on this.

 

[schmee]

Some rectifiers are taller than 3", keep that in mind. 5U4GB, 5R4, 5V4 etc

 

[King Fan]

I'm going to build the head cabinet just wide enough for one of the Hammond chassis boxes but how much room should I leave from the top of the chassis to the top of the cabinet?

Nice work, BTW. Re internal height, what @corliss1 and @schmee said. I think you're on the right track.

I recently had similar questions that got a nice discussion here. Just make sure you allow for any jokers in the deck -- allow for the pins on the tube, of course. And as mentioned, some NOS or other oddball or alternate rectifier tubes can be taller than others. Preamp tubes with shields (or just in sockets that have collars for shields) need to be pulled out further before you can extract them. Ever try to pull a tight tube using only 'wrist' force?

 

[rdjones]

I made some nice 1x12 speaker cabs and an amp head for an upcoming 18w TMB project and have enough lumber and tolex left to make another small head. I'm thinking I'll build a RobRobinette.com's Bassman Micro head (https://robrobinette.com/Deluxe_Micro.htm).

I'm going to build the head cabinet just wide enough for one of the Hammond chassis boxes but how much room should I leave from the top of the chassis to the top of the cabinet? From what I gather, the rectifier tube and power transformer will probably stick up the highest, just under 3". Should I go for about 5" clearance between the chassis top to the underside of the top of the cab?

Here's how my other cabs turned out. I'll probably build the micro head in a similar style though I'm not sure if I'll do the welting on the top or not. I'll use probably just a simple black leather style handle instead of the Marshall-style handles.
View attachment 981977 View attachment 981978 View attachment 981979 View attachment 981980

The link leads to the Deluxe Micro, but both it and the Bassman Micro appear to use the EZ81 rectifier which is not much taller than some of the 9pin choices for output tubes such as the 12BH7.
The concern arises if you use an octal rectifier, particularly one of the ST bottles.
Plan around the worst case scenario of the tallest rectifier, and add about an inch and a half to allow for insertion/removal.

 

[joulupukki]

The link leads to the Deluxe Micro, but both it and the Bassman Micro appear to use the EZ81 rectifier which is not much taller than some of the 9pin choices for output tubes such as the 12BH7.
The concern arises if you use an octal rectifier, particularly one of the ST bottles.
Plan around the worst case scenario of the tallest rectifier, and add about an inch and a half to allow for insertion/removal.

Sounds good. Since I plan to stick with an EZ81 (or similar 9-pin) I'll design around that. Thanks for pointing out that I posted the wrong link. I was debating between the Deluxe or Bassman Micro (definitely leaning towards Bassman).

 

[joulupukki]

Ok, so how’s this look? If I leave about 1 1/2” above the tallest tube (EZ81 rectifier) and my chassis is 2” tall, that’d be 6 1/2” inside dimension. The chassis (Hammond 1444-1372) is 13” wide. The front panel will overlap the chassis by 1/4”. This should be a much more simple amp head cab to build than the one for the 18w project.

 

[jman72]

Here's the inside of my Champ head cab I built. Only 1 inch between the transformer and the cab, but my tubes are horizontal.