5B4/5C4/5C5 Build

[olgoat]

I floated some questions on this a year ago and got side tracked.  http://www.el34world.com/Forum/index.php?topic=14041.0  Now I am back on track and ready to start my second amp build.  Again, thanks to all on the forum for making my first build, the 5E3, a success.  It sounds great.

I love the sounds that I have heard from the old V-Front supers.  There appear to be 3 circuits that were used 5B4, 5C4 and 5C5.   The layouts on the net for 5B4 are not very legible (the resistor values and small cap values are impossible to read).  But from what I can tell, the following are the big difference from 5B4 to 5C4

• Preamp section caps were .05uf (5B4) versus .1uf (5C4)
• There were 3 coupling caps (correct term??) totaling 60uf versus 4 totaling 64uf in the 5C4)
• Minor reduction in one of the resistors to the phase invertor 6sc7 (did I just sound stupid there?) from 7000 to 6800
  

For the life of me I cannot see any difference between 5C4 and 5C5.

I am pretty sure that the sound I like came from a 5B4 circuit.  What kind of tonal change if any would result from the capacitor size change in the 5C5?

These are the three layouts I am basing my question/comments on
5B4 https://app.box.com/s/lspv0fccmfj0o9tp7lcn
5C4 https://app.box.com/s/11eqsvwvqhoqv3buhyep
5C5 https://app.box.com/s/nfv4uthdwit3wasghq9n

Thanks for your time, guidance and comments.

[printer2]

The Super was originally the Pro.

http://ampwares.com/schematics/pro_5b5.pdf

[HotBluePlates]

The Super was originally the Pro.

Well, they were always the same amp but the Pro used a single 15, while the Super used a pair of 10's.

... old V-Front supers.  There appear to be 3 circuits that were used 5B4, 5C4 and 5C5.   ...

Leading "5" denotes 50's, middle letter denotes circuit revision, final # denotes model.

The Super is model #4, while the Pro is model #5. So the 5C5 is a schematic for the C-revision Pro.

For the life of me I cannot see any difference between 5C4 and 5C5.

You're proving my point. 

But look at the schematic for each, rather than the layout. See how the 5C5 has one speaker shown attached to the OT, while the 5C4 has 2 speakers shown? That (and the associated cabinet size) is the only difference.

When the Bandmaster came out, it shared the same circuit as these 2 amps, but had 3x 10's to distinguish it from the others.

...But from what I can tell, the following are the big difference from 5B4 to 5C4

• Preamp section caps were .05uf (5B4) versus .1uf (5C4)

Check

• There were 3 coupling caps (correct term??) totaling 60uf versus 4 totaling 64uf in the 5C4)

Filter Caps. The change to 16uF may just have been what manufacturers provided at the time. Notice that the first filter cap after the rectifier is 20uF in the 5B4, and 32uF (a pair of 16uF caps in parallel) in the 5C4. That gives a slightly cleaner, slightly higher B+.

• Minor reduction in one of the resistors to the phase invertor 6sc7 (did I just sound stupid there?) from 7000 to 6800
  
  Check; again, probably change from old value series to new value series, making 6.8kΩ the closest standard value to the original 7kΩ
  

There's one other tiny change: the cap to ground from the Tone control went from 0.01uF in the 5B4 to 0.005uF in the 5C4.

I am pretty sure that the sound I like came from a 5B4 circuit.  What kind of tonal change if any would result from the capacitor size change in the 5C5?

The preamp 0.1uF's after the first stages would allow a little more low end. The reduced Tone control cap would tend to reduce the low end. They may be off-setting...

Speakers are going to influence your opinion of the amp sound heavily. Did you listen to an original 5B4 Super?

I not familiar enough with new speakers to tell you if any capture the sound of a 50-year old set of originals. Then again, maybe you'll prefer something a new speaker has to offer.

[printer2]

The Super was originally the Pro.

Well, they were always the same amp but the Pro used a single 15, while the Super used a pair of 10's.

Just thought it might be helpful to know the amplifier section was the same and you can look at the Pro schematic rather than a Super layout where the part values are hard to read.

[HotBluePlates]

I see... Yep, you were on target with that.

[olgoat]

Thanks for the insights and comments.  It never occurred to me that they would have two different names for the same circuit because they were going into two different models. Interesting.

Kinda looks like I will give the 5B4 a try.  Try out Dougs board maker program to get started.

All the best to you guys.

[olgoat]

As far as speakers go I gotta say so far I am in love with Tone Tubbys, either the 50 watt alnicos or the low watt alnicos.  Amazingly broad spectrum of sound.

[Willabe]

I love my Tubby Tone 12" hemp cone alnico 50w.


             Brad     

[olgoat]

Starting to put the parts order together to build the 5B4 circuit per the above links.  (I have not been able to find a schematic for the 5B4 circuit, only a layout) 
5B4 https://app.box.com/s/lspv0fccmfj0o9tp7lcn
5C4 https://app.box.com/s/11eqsvwvqhoqv3buhyep

Some pretty big resistor value differences.

• across the bottom of the of the 3 filter caps the layout has 2 - 10M Resistors.  The 5C4 circuit has these as 10K.   Does that sound right?
• Across the top of the 25 ohm/10W resistor and the .05uf cap the 5B4 layout has a 250M resistor, the 5c4 has a 250K.  Same question.  Does that seem right?
• THe paired resistors going to pin 2 on each of the 6sc7s in the 5B4 is 250M, 5C4 has 250K.
• There is a 250M resistor paired with a 7000 ohm going to pin 3 of the phase inverter (correct term?) 6sc7. In the 5C4 it is a 250K
  

If these values are correct on the layout, what kind of change if any does a big change in resistance like this make at these points in the circuit?  Brighter/harsher tone with the higher values of the 5B4?

Thanks for any thoughts.

[sluckey]

Some pretty big resistor value differences.

Not really. During the time that amp was new, 'M' was still being used to represent 1000. Think Roman Numerals. 1,000,000 was spelled out as 1 MEG.

It's a little confusing but common sense should rule. There ain't gonna be any 10 megohm resistors in the B+ dropping rail for a guitar amp. And a 250 megohm resistor would just be an open circuit!   

[olgoat]

Thanks for the clarification.  I am a solder by numbers guy.  I am amazed when anything amp wise works.   Appreciate it.

[terminalgs]

what PT will you be using?   

I'm not a big fan of grid-leak biased 1st preamp gain stages (cathode grounded with a high grid leak). although, in fairness to this fender circuit, my experience has always been with bargain bin type amps that, perhaps were probably unimpressive regardless of this particular circuit nuance.

[olgoat]

I am looking at the Classic Tone PT from Magnetic Components40-18029 710V 200 mills.  The layout for 5b4 says 700V and 140 mills.  I believe the PT # was 6516 back in the day. 

[Willabe]

That PT might give too high a B+dcv, because of the extra 60mA.   


            Brad     



 

[olgoat]

Yeah I am concerned about that too. But I have not found anything that matches the mA and voltage specs. 

[olgoat]

Mag Components got back to me with an opinion on the PT.  They thought the 40-18029 at 710V 200 mA might be ok. They suggested one of their Marshall PTs as another possibility at 690v 150mA  40-18054.   A bit bigger than the 40-18029 but the chassis for the super is pretty good size so it might work. 

I'll have to see if I can find something on Hammonds site.   I am amazed that Mercury Magnetics does not have more specs available on their units for the price they charge.

[olgoat]

I totally missed the reference to 6516 on Mercury Magnetics.  Thanks for pointing that out.  I'd love to try their stuff but that is a chunk of change alright.

I checked with Heyboer and they say their PT for 5B4 is
"Primary = 120v
Secondary  370-0-55-370 @ 300 ma
                6.8 v @ 3A
                5.4 v @ 3A

Our part # is HTS-4831"  

So that current output is even higher than Magnetic Components Classic Tone 40-18029 at 355-0-255 at 200mA

Weber for the 5C5 bill of material uses their 35130 which is 340-0-340 150mA

The Magnetic components Classis tone 40-18029 says the B+ with a 5U4GB (my layout calls for a 5U4G) is 373V DC.  I am thinking that is the way to go.  A little on the high side but not as high as some of the other alternatives.. It can also be wired for 305-0-305 so maybe it could be used if I try to switch the output tubes to 6V6s if there is too much power from the 6L6s.

[terminalgs]

If your filter caps are all rated 450-500V,  I wouldn't worry if instead of 373V HT, you end up with 390V or even 400V.

[olgoat]

I was going to use the sprague 20uf rated at 500V.