First build! Chassis layout ok?

[larstore]

Hello!

Getting ready to drill the chassis for for my first build, a 18W Hoso56 style amp in a 17 x 2.5 x 6.5 hoffman chassis.

Read every possible article on layout and component placement, and would be very happy for any input to the following sketch!

Thanks in advance,
LT

[Willabe]

Hi and welcome!

You do not want the power and standby switch next to the input jack.

Keep all the hi voltage/hi current stuff on the far side of the chassis away from the low voltage/low signal stuff.

Scroll down to the very bottom of this page and go into out host Doug's tube amp library of schematics and look at some Fender layout schemos and see how they layout their amp chassis.


                   Brad        

[eleventeen]

I think you're asking for big time trouble. No way should you put power & stdby near the input jack.


You should IMO either pre-drill holes to mount the OT 90 degrees (total of four holes) or not drill any holes and be prepared to rotate the OT 90 degrees if it's necessary to reduce him. It will be very tricky to drill those holes after you get the amp assembled.


I have to say I would consider mounting the input jack sort of in the center of the front panel and getting the tone controls and first gain controls at the preamp tube end. Your "early-preamp" controls near the choke & p/s are in the worst possible spot. I am trying to mentally reformulate the scale of your dwg.


No matter what, you cannot put power and stby anywhere near the input. That will kill you.

[larstore]

Willabe!

That make sense :) Thanks!
Moved it to next to the PT and attached the new layout. Any input on transformer and tube placement?

[larstore]

You should IMO either pre-drill holes to mount the OT 90 degrees (total of four holes) or not drill any holes and be prepared to rotate the OT 90 degrees if it's necessary to reduce him. It will be very tricky to drill those holes after you get the amp assembled.

The OT is placed kind of randomly (but away from the preamp as much as possible)
I was thinking about trying the "headphone" trick first, but drilling 4 holes is a good idea! Thanks

[Willabe]

I'd probably lay it out like a Fender.

I'd move the SS rectifier either in line with the power tubes at the far end of the chassis or make a small eyelet/turret board for it in side the chassis. I might move the power tubes a little towards the phase inverter (PI) tube. 

I might move the OT more towards the chassis center, from front face to back face.

Look at some Fender layout schemos.


                    Brad     

[Willabe]

If the 3 pink circles on the back face by the output tubes are speaker jacks I'd move them closer to the OT inbetween the power tubes and PI tube.


                   Brad   

[larstore]

Willabe!

Thanks again. Found some fender layouts, and they say the same as you, so i moved stuff around.
Is a separate turret board for the rectifier really necessary? I moved it inline with the power tubes for now.

And, labeled the speaker jacks ;)

Attached the new layout. Any input appreciated!

[Willabe]

Is a separate turret board for the rectifier really necessary? I moved it inline with the power tubes for now.

No a separate turret board for the SS rectifier is not necessary.

I take it your going with a SS rectifier that plugs into a tube socket?

Either way works. Sometimes you don't have the space for an extra socket in the chassis.


                                Brad   

[larstore]

I take it your going with a SS rectifier that plugs into a tube socket?

Yes i am :)

So, the last layout looks good?

[Willabe]

Found some fender layouts, and they say the same as you, so i moved stuff around.

No I'm going by how they laid out their amps.   

Why try and reinvent the wheel? Copy from proven known working circuits and layouts, then adjust as needed, if needed.

There are reasons they did what they did. I only brought up Fender because they have layout drawings for their amps. If you look at other amp companies builds a lot if not most are laid out the same. AC power, hi voltage/hi current kept on 1 end of the chassis and input low voltage/low current/small signal kept on the other side to isolate the small signal from being disrupted by the hi power stuff.



                         Brad      

[Willabe]

So, the last layout looks good?

Looks pretty good to me but lets see if anybody else sees something I'm not?


                  Brad   

[Willabe]

I guess your going with a multi tap OT secondary and that's why you have 3 speaker jacks?

You could save a little space if you used a 3 Way rotary impedance switch. Doug sells a good 1, here's a link, just scroll down to see it;

http://hoffmanamps.com/MyStore/perlshop.cgi?action=template&thispage=Switches&ORDER_ID=431845458

I'd probable flip/flop the power switch with the standby switch, but you don't have to.

             
                          Brad   

[Willabe]

Is your Fx loop passive? And what's the ft. switch jack for?

You might need to move the Fx loop a little more away from the input preamp tube. Are you putting the Fx loop right before the PI?

Maybe move the ft. switch to the input side, so the order would be ft. switch, Fx loop send/out, Fx loop return/in.


                        Brad      

[Willabe]

Can you post a schematic for this build? That would help.


                  Brad   

[Willabe]

You should rotate the choke 90 degrees so it's core is not parallel to the OT's core, so they don't couple, ie, noise. You PT is a lay down right? If so then all 3 pieces of iron's cores will be on different planes for least noise.


                      Brad       

[tubenit]

Can you post a schematic for this build?

This is Geezer's original HoSo56 but with a PPIMV (LarMar) added.

with respect, Tubenit

[Willabe]

Thanks Tubenit.


             Brad   

[larstore]

Is your Fx loop passive? And what's the ft. switch jack for?

The foot switch is actually combined into the FX loop on the schematic (tubenit posted, thanks!), but i want a separate footswitch.
It changes between the "pseudo channels" shown in the schematic.

You could save a little space if you used a 3 Way rotary impedance switch. Doug sells a good 1, here's a link, just scroll down to see it;

I have had amp issues when people just leave the impendance switch and plugs it into a new cabinet.
With separate jacks, atleast they have to make a decision when plugging in :)

I'd probable flip/flop the power switch with the standby switch, but you don't have to.

I will, i just copied and pasted it now for drilling

You should rotate the choke 90 degrees so it's core is not parallel to the OT's core

Thanks. I read somewhere that it should not matter, but i will first mount the PT, and use a oscillioscope to check placement of OT and Choke before drilling


Thanks again!

[tubenit]

It changes between the "pseudo channels" shown in the schematic

Are you doing Geezer's  HoSo56 II with pseudo channel switching??

With respect, Tubenit

[larstore]

Are you doing Geezer's  HoSo56 II with pseudo channel switching??

Yes! Finished the turrent board, and getting ready to drill the chassis as we speak.
I understand you've been very much involved in the reverse engineering process back in the days? Do you have any suggestions?

LT

[tubenit]

Geezer's HoSo56 is a fantastic amp!!  I love it.  And he pretty much got it "right" from the git go.

Only a couple of values to experiment with.  I highly recommend the "enhance" cap because it smooths out the high end "hash" noise for a smoother sounding amp, IMO.

With respect, Tubenit

[sluckey]

Will you be using any multi-cap cans or just individual caps?

I'd be tempted to do this...

[larstore]

Will you be using any multi-cap cans or just individual caps?
I'd be tempted to do this...

I will be using individual caps.
So you would move the choke behind the PT, and the rectifier closer to the PI tube? Any good reason? ;)

[Willabe]

If you look at Geezers layout drawing you can see he has the front face panel controls arranged in order to keep the wire runs to the controls short and not crossing over each other as much as possible.

I'd go with his layout including where he has the FX loop jacks because his is known to work as he built it.


                   Brad   

[larstore]

If you look at Geezers layout drawing you can see he has the front face panel controls arranged in order to keep the wire runs to the controls short and not crossing over each other as much as possible.

I know, but it just makes so much more sense to have the two channels controls grouped together.
Would it really cause that much headache if a couple of pot wires crosses eachother?

[Willabe]

Would it really cause that much headache if a couple of pot wires crosses each other?

Yes it might. And it's not just pot wires crossing it also adding length to grid wires in the tone stack (TS) and to/from the gain/volume pots. Any wires after a plate coupling cap going to the next grid is a grid wire and those need to be as short as possible with in reason or they need to be shielded cable, shield grounded at 1 end only.

I know, but it just makes so much more sense to have the two channels controls grouped together.

Yes to you it does but not to the circuit. And if it doesn't like it, it will tell you by causing problems. 



                   Brad   

[tubenit]

Guys,

As an FYI .......... the layout drawing in the Hoffman style is actually my drawing and NOT how Geezer actually did it.  It simply made sense to me to draw it up that way.

I think Brad has a good point about shorter wires and not crossing too much.  IF you choose another route, then you can use longer wires with shielding for one of the gain and one of the trim & hopefully leave the other not shielded.  Since the shielding does add a little capacitance and lessen highs .......... I probably would be more prone to shield the pseudo channel that has more gain & let the capacitance help smooth the highs.

If you're comfortable sharing, I'd love to see some chassis inside shots of the progressing work when you can share them?

Just a thought.  With respect, Tubenit

[larstore]

Yes to you it does but not to the circuit. And if it doesn't like it, it will tell you by causing problems. 

I'll change it :)

If you're comfortable sharing, I'd love to see some chassis inside shots of the progressing work when you can share them?

I'll do that!

[Willabe]

IF you choose another route, then you can use longer wires with shielding for one of the gain and one of the trim & hopefully leave the other not shielded.  Since the shielding does add a little capacitance and lessen highs .......... I probably would be more prone to shield the pseudo channel that has more gain & let the capacitance help smooth the highs.

This sounds like a good option to me.

Tubenit's built a LOT of amps and knows what he's talking about.


                         Brad   

[larstore]

Tubenit,

How did you layout the internals when building the hoso56?

This sounds like a good option to me.

As this is my first build, i'll stick with the already tested option.

[Willabe]

As an FYI .......... the layout drawing in the Hoffman style is actually my drawing and NOT how Geezer actually did it.  It simply made sense to me to draw it up that way.

I assumed that the layout T posted was Geezer's layout drawing that he used, but I was incorrect in assuming that, but....

Tubenits built more than enough amps to have a good understanding on what will more than likely work in a layout.


                 Brad