Tame new speakers for a 5f4

[Ed_Chambley]

I have gotten some new speakers in a new 5f4 build and it really is LOUD. They are Weber recones and I am assuming they are not extremely efficent.  It is a combo, but I can run a Ab764 Super Reverb to them and they have a nice early break-up.  I like the sound, but cannot get it to a usable volume at break-up.  Can anyone give me an idea of how to install PPIMV or any idea of how to tame this beast.  I have tried a couple of different MV's, but they lack bottom until cranked.  Stock, it has an extremely nice clean with plenty of low end.

[HotBluePlates]

Am I reading you right that the 5F4 is too clean/loud with the speakers you have, but feeding the same speaker with a Super Reverb is getting distortion at a lower volume level?

[Ed_Chambley]

Am I reading you right that the 5F4 is too clean/loud with the speakers you have, but feeding the same speaker with a Super Reverb is getting distortion at a lower volume level?

That is the case. I do not understand it.  I have 4 different 5f4 builds and this one is a combo.  The others are heads.  Only one is stock.  I have never found a master volume that works well with a 5f4.  The speakers really do sound great as weber took some old CTS, 1.5 inch voice coils, 40 watt, 16 ohms running at 8 ohms.  The other 5f4's I have breakup with these speakers, but I built this 5f4 with a Mercury Magnetics Supro Axium OT.  Here in lies the difference I would think, but I cannot find a good master volume for it or just don't know how to install it.  It is clean almost to the point of a twin.  If I put a catlinbread formula 5 in front, it is not bad, but it is still LOUD to reach the sweet spot.  I just tried the 1 meg single pot master from the trainwreck pages and I have lots of static so must not have it correct.  I don't even know if a master will work well so I guess I will go to a vvr next if I cannot find a master that will work or just simply have a very clean 5f4.  I did add a .68 cap with a 4.7 resistor to the normal o jump the channels.  It sounded petty cool, but now I will have to remove the master.

[HotBluePlates]

I have a 5F4 copy, too, and it should be a loud, clean amp. The Super Reverb should be louder, though, all things being equal.

So maybe they're not equal. Alright, we'll add a master volume.

I just tried the 1 meg single pot master from the trainwreck pages and I have lots of static so must not have it correct.  I don't even know if a master will work well so I guess I will go to a vvr next if I cannot find a master that will work or just simply have a very clean 5f4.

The master volumes on the Trainwreck pages don't work with a split-load inverter. Some of them also need caps on either the input or outptut to keep d.c. off the pot; d.c. (from either the phase inverter output or from the output tube bias) will cause the scratchy sound.

Find pin 7 of the phase inverter, and follow it back to the board. There is a 1M resistor there. Unsolder the wire at the 1M end, and remove the 1M resistor.

Take a 1M pot, and look at the back of it with the solder lugs pointing up. You will run a wire from the eyelet that previously held the wire from pin 7 and one end of the 1M resistor. The wire from pin 7 will run to the center lug (you will likely have to extend or replace the wire). The left leg goes back to the board, to the junction of the 56k and 1.5k resistors.

The master volume replace the 1M resistor, which previously bootstrapped the input of the split-load inverter. You will keep the same apparent load for the previous stage, but will be able to tap off a smaller signal voltage when you turn the master down.

I haven't tried this master with this amp, so I don't know how good it will sound. This is the typical method to apply a master volume to the split-load. My concern about whether it will sound good is that there is some feedback from the tone circuit to the second gain stage. I'm not sure how that will react as you start to approach overload in the preamp.

[Ed_Chambley]

Thanks for the input.  Just to be clear, I will only have 1 wire connected to the pot center, then ground the pot.

I know what you mean that the amp should be loud and clean.  My others are, but this one is simply over the top.

[sluckey]

The left leg gets grounded, however you have that done in your amp.

No! The left lug connects to the junction of the 1500 and 56K in the cathode circuit (V3-8).
 

[Boots Deville]

From his description, it sounds like HotBluesPlate is describing the 1M pot wired as a variable resistor, replacing the 1M resistor.

The attached image was posted by FYL in this thread:
http://www.el34world.com/Forum/index.php?topic=12365.msg114948#msg114948
where he states that in his experience it is "transparent at all settings".

This shows a slightly different arrangement. 

With the FYL version, the pot setting is going to effect the value of the "grid stopper" whereas with the HBP version, the grid stopper stays constant.

It would be a simple task to switch between the two and let my ears be the judge, but are there any opinions on which works better?

-John

[HotBluePlates]

From his description, it sounds like HotBluesPlate is describing the 1M pot wired as a variable resistor, replacing the 1M resistor.

I'm too young to be able to blame it on a senior moment, but that's what happened!

Sluckey told you right, and Boots' diagram based on FYL's suggestion is what I had in mind. I revised my earlier post to provide the correct information.

[Ed_Chambley]

OK, I put a 1 meg pot in and removed the resistor. 2 wires to begin with.  With the newly installed master volume turned all the way down it does not silence the amp.  It does however reduce the volume.  In turning up the pot only the first 1/8 turn has any effect.  It is an audio taper, but reading it with a mm it is nowhere near 1 meg when the amp is at full volume.  Seems to reach full volume at about 250k and from 250 to 1 meg there is no audible difference.  I also added a third wire going to the .02 cap and also no noticeable difference.  It does work somewhat as a master volume, but it is closer to a switch.  Is this what is expected?  I thought this would be simple, but there I go thinking again.

What I did.  I removed the 1 meg resistor.  Wired the center lug to the same eyelet where pin 7 of the PI connected.  Where the other end of the resistor was I wired the right lug.  Tested this and the results were as I explained above.  Added the third wire just out of curiosity and it made no difference.

[sluckey]

Do it like this...

[Ed_Chambley]

Do it like this...

That makes perfect sense, duh!  Thanks!  With the underboard wiring I actually have the center and left lug connected together.  You want to know how to make something simple very hard, just ask me.

[Ed_Chambley]

Do it like this...

Well I wired just like this last night and it still will not silence the amp.  I have static as well.  I may have a bad pot.  It checked fine with my mm, but I am planning to change it out tonight. With the pot full open the amp is quieter.  If changing the pot does not help, is there anything else I can try.

[sluckey]

I never really thought that circuit would totally 'silence' the amp. If you want a simple MV that will silence the amp, do it like this. This one will absolutely kill the sound when you turn it to zero.

[Ed_Chambley]

I never really thought that circuit would totally 'silence' the amp. If you want a simple MV that will silence the amp, do it like this. This one will absolutely kill the sound when you turn it to zero.

Silencing is not necessary.  I have to just determine where the static is coming from.  I did use an old pot and I have a habit of keeping bad parts. Thanks for the new schematic, I may give it a try, but I think I should work out the current static problem.  I have no idea where it could be coming from if not the pot.

[sluckey]

There is approx 50 volts on that pot, but if it's wired like my drawing there's no path for dc current flow. That means there would be approx 50 volts on every lug of the pot. I'd think there would be no static with same dc voltage everwhere. I could be wrong. I have no actual experience with that circuit.

[Platefire]

I have two 5F6-A Bassman Head Builds. One is a Dukane PA and the other is a Bogen CHB-50 PA. That looks like the same Cathode follower arrangement as mine. I've been thinking of installing a MV on those builds--would that arrangment work for mine? Due to lack of space for controls, I would have to pull the existing volume control and install a stacked two-one meg pot. Platefire

[sluckey]

Here's a better drawing of the next gen master volume. I never said it before but my intent was to pull the ext speaker jack and mount the MV pot in that hole. Should be very convenient.

Platefire, we're not looking at a cathode follower in this 5F4. We're looking at a split load PI (partial schematic). I don't think this MV is suitable to your 5F6A.

[Platefire]

OK, Sorry. Guess thats for another project, another post.

[sluckey]

Platefire, I'd do that 5F6A like the Marshall JCM-800 2204. See pic...

[Ed_Chambley]

Here's a better drawing of the next gen master volume. I never said it before but my intent was to pull the ext speaker jack and mount the MV pot in that hole. Should be very convenient.

Platefire, we're not looking at a cathode follower in this 5F4. We're looking at a split load PI (partial schematic). I don't think this MV is suitable to your 5F6A.

To test it, could you just lift the cap leaving the underboard wire?  On this build, getting to the underboard wiring is a real pain.

[sluckey]

To test it, could you just lift the cap leaving the underboard wire?

Yes. In fact, just remove the .02 cap and then connect the cap directly between the mv pot and the tube socket. You would end up with 2 caps between the pot and tube socket. If your layout is different from the orig. Fender layout, you'll have to figure out something different. I've been assuming your layout is the same. Is it???

[Ed_Chambley]

To test it, could you just lift the cap leaving the underboard wire?

Yes. In fact, just remove the .02 cap and then connect the cap directly between the mv pot and the tube socket. You would end up with 2 caps between the pot and tube socket. If your layout is different from the orig. Fender layout, you'll have to figure out something different. I've been assuming your layout is the same. Is it???

the layout is the same except for an adjustable bias and the OT is different.  The cap on the bass pot is different.  Some minor differences, but the board is the same as the fender layout.  Orange drops for the .1's, mallorys on the board and sozo in the tone stack.  CC resistors until you reach the phase inverter.  There are carbon film.  Shielded wire to v1 and the addition of a .68 and 2.7 for the normal channel.  Kind of nice change for the normal channel.  Some other things as well like relays instead of fuses.  That kind of thing.  I have a fat switch for switching different values of Silver Micas in the tone stack for some variety.  Nothing major.  I do have a extra tube socket with heater wires to it.  I put it in for a possible future use of maybe a tremelo or reverb or even an additional gain stage.  No current plans for it, but put it there as I had plenty of room in the chassis.  It is actually my experimental amp as I have 3 more 5f4 head versions.  Love the 5f4, but I am really getting interested in the TOS you guys have made.  I will be making a Stout next, then probably a TOS, I really think this is a brilliant idea.