The Amp Garage Forum Index The Amp Garage
A tube amp builder's community
 
 FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 

How to Mount Power Transformer on Chassis?
Goto page 1, 2  Next
 
Post new topic   Reply to topic    The Amp Garage Forum Index -> Technical Discussion
View previous topic :: View next topic  
Author Message
The New Steve H



Joined: 30 May 2011
Posts: 935

PostPosted: Fri Jun 03, 2011 12:14 am    Post subject: How to Mount Power Transformer on Chassis? Reply with quote

Today I machined a big hole in my homemade amp chassis and stuck a power transformer in it. This is a 5f6a clone.

I have a question.

The transformer has some kind of plastic shields on the screws that hold it together. These are the same screws that attach it to the chassis. There are four of them. One of them has no insulator on it, and it has a toothed washer on it. I assume it's for the ground.

Am I supposed to put the washer between the transformer and the chassis, to keep it level (to compensate for the lack of an insulator), or should I put it on the other side of the chassis, under the nut? If I do it the latter way, the transformer will not be level.

_________________
Relax. It's SUPPOSED to smoke a little.
Back to top
View user's profile Send private message
M Fowler



Joined: 16 Jan 2008
Posts: 10821
Location: MN

PostPosted: Fri Jun 03, 2011 12:24 am    Post subject: Reply with quote

The transformer bolts should have came tightened already and you run those mounting bolts through the chassis and use a washer with either nylock nut or keps nut.
Back to top
View user's profile Send private message Send e-mail
The New Steve H



Joined: 30 May 2011
Posts: 935

PostPosted: Fri Jun 03, 2011 12:29 am    Post subject: Reply with quote

Um...are you saying I made a mistake by removing the nuts so I could use them to fasten the transformer to the chassis? I'm supposed to go get four more nuts?

I guess this would explain why they were so tight...

_________________
Relax. It's SUPPOSED to smoke a little.
Back to top
View user's profile Send private message
Cliff Schecht



Joined: 30 Dec 2009
Posts: 2599
Location: Seattle

PostPosted: Fri Jun 03, 2011 12:32 am    Post subject: Reply with quote

No it's not a big deal that you removed those. Just crank em down tight again (don't strip them though!). I don't float the transformer above the chassis like you mention. I remove the bolts, drop the tranny flat against the chassis, put the bolts back in and crank em down..

Now quit thinking so much and build your amp already Steve! Maybe that physics degree did hurt more than it helped Razz.

_________________
Cliff Schecht - Circuit P.I.
Back to top
View user's profile Send private message Visit poster's website
The New Steve H



Joined: 30 May 2011
Posts: 935

PostPosted: Fri Jun 03, 2011 12:34 am    Post subject: Reply with quote

Hey, I can't help it. Those insulators hold three corners of the transformer a millimeter off the chassis, and the groundy corner is flat against the metal. Tell me that wouldn't drive you nuts.
_________________
Relax. It's SUPPOSED to smoke a little.
Back to top
View user's profile Send private message
Cliff Schecht



Joined: 30 Dec 2009
Posts: 2599
Location: Seattle

PostPosted: Fri Jun 03, 2011 12:40 am    Post subject: Reply with quote

Can you not get rid of the washers? I always get rid of anything insulating the transformer from the chassis. I do use washers transformers where the screw meets the top of the transformer and where the bolts hit the chassis but there shouldn't be washers in the way anywhere else. This is why I keep spare transformer-sized screws around.
_________________
Cliff Schecht - Circuit P.I.
Back to top
View user's profile Send private message Visit poster's website
The New Steve H



Joined: 30 May 2011
Posts: 935

PostPosted: Fri Jun 03, 2011 12:42 am    Post subject: Reply with quote

I want to keep the insulators because I read that a transformer should only be grounded to the chassis at one point. I guess I could put a conductive washer under the low corner.
_________________
Relax. It's SUPPOSED to smoke a little.
Back to top
View user's profile Send private message
M Fowler



Joined: 16 Jan 2008
Posts: 10821
Location: MN

PostPosted: Fri Jun 03, 2011 12:43 am    Post subject: Reply with quote

There are a few ways to mount the PT.

But yeah after I get a PT in the chassis I use four more nuts, washers and tighten it down.

Those plastic sleeves should be in further?
Back to top
View user's profile Send private message Send e-mail
David Root



Joined: 04 Aug 2006
Posts: 3009
Location: Lower Mainland BC

PostPosted: Fri Jun 03, 2011 12:45 am    Post subject: To Float or not to float Reply with quote

That's not something I ever thought about to be quite honest.

I have bought transformers that were fully bolted up and came with a set of locknuts for bolting up to the chassis ie "floating". (I assume we are talking about laydown arrangement here).

Is there a sound reason for not doing it that way?

Update. I checked some of my stock transformers.
Two Magnetic Components 40-18024 laydown BF Twin have nylon bolt insulators that DO insulate the PT body from the bolts.
One Mag Cpts Marshall 100W STANDUP OT 40-18026 also has what appear to be the same nylon bolt insulators but is NOT insulated from the mounting bolts.
One NOS Fender Bassman 70 laydown mounting bolts have washers on them and the mounting bolts are NOT insulated from the PT body.


Last edited by David Root on Fri Jun 03, 2011 1:05 am; edited 2 times in total
Back to top
View user's profile Send private message
M Fowler



Joined: 16 Jan 2008
Posts: 10821
Location: MN

PostPosted: Fri Jun 03, 2011 12:48 am    Post subject: Reply with quote

Some people don't want the amp floating on top of the nuts and others want to isolate the PT from the chassis.
Back to top
View user's profile Send private message Send e-mail
Cliff Schecht



Joined: 30 Dec 2009
Posts: 2599
Location: Seattle

PostPosted: Fri Jun 03, 2011 12:56 am    Post subject: Reply with quote

Floating on nuts with thin aluminum is asking for problems, so I don't do it on flimsier chassis. Aluminum doesn't help or hurt with shielding but I thought steel chassis couple the stray flux on a laydown PT (hence why Fender usually put the OT pretty far from the PT).
_________________
Cliff Schecht - Circuit P.I.
Back to top
View user's profile Send private message Visit poster's website
David Root



Joined: 04 Aug 2006
Posts: 3009
Location: Lower Mainland BC

PostPosted: Fri Jun 03, 2011 1:07 am    Post subject: Reply with quote

So this is a mechanical rather than electrical issue?
Back to top
View user's profile Send private message
The New Steve H



Joined: 30 May 2011
Posts: 935

PostPosted: Fri Jun 03, 2011 1:36 am    Post subject: Reply with quote

Wow, it sort of looks like this wasn't a totally stupid question.
_________________
Relax. It's SUPPOSED to smoke a little.
Back to top
View user's profile Send private message
diagrammatiks



Joined: 27 Mar 2011
Posts: 558

PostPosted: Fri Jun 03, 2011 1:44 am    Post subject: Reply with quote

I always thought that the one place rule was about the grounding of the center tap or the reference of the rectifier.

The old fenders had the laydown drop through pt's. I don't think those were completely isolated since they sat a bit inside the chassis.
Back to top
View user's profile Send private message
David Root



Joined: 04 Aug 2006
Posts: 3009
Location: Lower Mainland BC

PostPosted: Fri Jun 03, 2011 3:50 am    Post subject: Reply with quote

I don't recall the original Fender PTs having insulating shoulder washers on the mounting bolts.

I can pull the chassis on a '67 AB165 Bassman & check but that is a PITA. Anyone happen to know "fer sure"?

But those two new Mag Cpts Twin PTs I have are "fer sure" insulated from the mounting bolts!

I can see if you had a winding short to the core you might not want it (the core) grounded to the chassis, OTOH isn't that why they have bells so that the electromagnetic emissions ARE grounded to the chassis?


Last edited by David Root on Fri Jun 03, 2011 3:59 am; edited 2 times in total
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    The Amp Garage Forum Index -> Technical Discussion All times are GMT
Goto page 1, 2  Next
Page 1 of 2

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You cannot download files in this forum


Powered by phpBB © 2001, 2005 phpBB Group