Manzamp!

[10thTx]

I get the following message when I tried to access the layout and schematic: The selected Attachment does not exist anymore

IF you have the ExpressSCH program to open it, it should open right up. It does for me on two different computers.

With respect, 10thtx

[Chad]

I get the following message when I tried to access the layout and schematic:

The selected Attachment does not exist anymore

I seem to get that also with all the editable schematic posted here and at Hoffmans forum

[Chad]

I get the following message when I tried to access the layout and schematic: The selected Attachment does not exist anymore

IF you have the ExpressSCH program to open it, it should open right up. It does for me on two different computers.

With respect, 10thtx

I thought that I did but will check to make sure.Thanks,Chad

[ic-racer]

Very nice sounding amp IC!! And...wonderful job as always Jeff on the documentation.

Forgive me for not reading through the whole thread looking for an answer...but I noticed that the schematic does not identify grid stoppers on the power tubes.

Is that by design?

Again....really great stuff guys and many thanks for sharing!
Dave O.

Good question. A little of the mystery of the amp. I don't see them in the picture, assuming he would have had them sticking up like he did with the EL34 HRMs, but that is not to say they are not there.

Speaking of other things that may be hidden. There may be diodes on the rectifier tube socket. As it stands, the first capacitor is too big and the GZ34 resistors are too small based on the historical recommendations. Having said that my GZ34 does not spark but occasionally has a small one when the standby is flipped.

[ic-racer]

It makes the EL34 plate and screen too high,

520v on the plates of an EL-34 is not that high ( Early Marshall Plexi voltages)..I would leave a 22k in there and find out why it blew.. Perhaps you have a bad 34!

With 518 on the screens a 22k should get you under the 300v max rating 12ax (50v cathode)range on the PI (w/24k tail) Music Man Dumbles (same PI) running 700v use a 47k dropper there..Cathode follower should be sitting somewhere between 150-180v

Tony

Thanks for your comments, lets look into it. What I was thinking is that the screens might be too high, what do you use as a high limit on screen voltage?

The fuse failure was associated with about 15 minutes of playing when it suddenly lost some gain. It got better or about 5 minutes then it happened again and the fuse went. No sparking, red plate, smoke, hot components or any visible signs of badness.

So with a dropping string of 22k, 10k, 5k the voltages were
EL34 Plate 520V (I did not measure the screen)
EL34 cathode current was set to 30ma at that plate voltage
V1b Plate 224
V1b Plate 230


In terms of the schematic I posted.
The main reason I'm doing the project is because of this forum. For example, my wife was less than impressed when I brought her into the basement to see the naked MANZAMP chassis in all its glory sitting on the floor among a mass of wires ( "...thats it? ") If not for the ability to share the build on this forum I'd really not have much reason to even do this.

In terms of commercial enterprise, I was joking with myself that I was going to time it from the moment I posted the schematic to the appearance of a Ceriatone Manzamp. But seriously, the schematic I posted will need a lot of re-working to be sold as a commercial product.

Bottom line is I think it would be great to see any of the commercial builders engineer this into a viable product to sell.

My main interest the Manzamp is academic. I want to try and figure out more about how Dumble designed and built his amplifiers.

[talbany]

For anything over 500v on the screens of a 34 I try to stick with the JJ's
and have no real trouble loading these in those old HV Marshalls' and the Traynor YBA Bassmasters..(560v)
However!!..The EL34 screen supply's are (compared to a 6L Beam) wimpy..This always seemed quite odd that they can dissipate 8w (@450v) and how many screen resistors have we had to change on a 34 amp..
I also find that 34's are more prone to drifting so I always try to monitor them for at least 15 min or so and usually have to tweak the bias supply..If you start chewing through 34's I would look at going to a 5U4..This would drop about 30v as well as give you a bit more sag!!

Bottom line is when ever you go over the Max rating it's a crap shoot..If it's a well built supply in that tube it should hold up!!.. If not it will usually go within the first 10 hrs of operation..BTW with the 22k in there what are you getting at the plates of the PI?

Sorry I couldn't help further!!

Good Luck!!

Coming soon Ceriatone Mansamp!!

Tony

[ic-racer]

I tried 2k2, 22k, 5k and while writing down the voltages I had a little fire works display in the rectifier tube and another blown fuse.

So, on investigation I find the following. Now shoot me for not recording all these values when I powered up the first time. So I don't know if there is a problem or not.

I measured the voltage on the Gz34 socket (no tube) and got different values on each side. The resistors both read 5r with essentially no drop across each as expected with no tube in the socket.
318vac
420vac

So, I measured the OT secondary resistance and they are different:

49 r
32 r


GZ34 "EICO emission" measures 10% "units" different on the two sides. Maybe one side sparked more than the other? Who knows what the emission test means in this setting anyway.

My concern is a short across some of the windings of the secondary of my PT.

[talbany]

I tried 2k2, 22k, 5k and while writing down the voltages I had a little fire works display in the rectifier tube and another blown fuse.

So, on investigation I find the following. Now shoot me for not recording all these values when I powered up the first time. So I don't know if there is a problem or not.

I measured the voltage on the Gz34 socket (no tube) and got different values on each side. The resistors both read 5r with essentially no drop across each as expected with no tube in the socket.
318vac
420vac

So, I measured the OT secondary resistance and they are different:

49 r
32 r


GZ34 "EICO emission" measures 10% "units" different on the two sides. Maybe one side sparked more than the other? Who knows what the emission test means in this setting anyway.

My concern is a short across some of the windings of the secondary of my PT.

A shorted sec you would be reading 0 Dead short..Those # look OK..Sounds like your rectifier took a dump!!

Tony

[ic-racer]

Thinking out loud here for some re-build plans.


1) increase the 6r 20W resistors to something closer to recommended specs for GZ34 (or bigger?)
2) put diodes on the gz34 socket (because I'm NOT going to lower the 110uf capacitance of the first node.
3) put a fuse between the PT and the GZ34

[ic-racer]

A shorted sec you would be reading 0 Dead short..Those # look OK..Sounds like your rectifier took a dump!!

Tony

Looks like I can muster up a few more GZ34s from other amps. I also have a few 5Y3s and 5U4s. Hmm maybe the Manzamp had 5u4? The RCA 5u4 in front of me is a much closer match to the picture, but I guess there were RCA GZ34s in the bigger bottle also.

[ChrisM]

110uF as the input/reservoir filter cap is really pushing that GZ34.

[Reeltarded]

It's not just pushing it. It's blowing it up.

[martin manning]

I wondered how much effect the 6R resistors (value on your schematic) in series with the rectifier would have. How did you arrive at that value? See here for some discussion: http://www.valvewizard.co.uk/fullwave.html

[talbany]

GZ34 It should be typically at least 150R for a 400V supply and a 60µF cap in a capacitor input filter. Source resistance is the sum of the PT reflected DCR and of any added series R between the PT and valve.

http://www.wooaudio.com/docs/tube_data/5AR4.pdf

Tony

[ic-racer]

RE: Rectifier tube into big capacitor

So what is Mr D to do?

I think he would have put the diodes in line with the rectifier supply from the transformer. I'm looking at the socket now and these seem to be easily attached to 'spare' lugs on the socket.

He may have added extra resistance in series beyond the suggested minimum. We don't know the value of those big green resistors.

So I just got back from RadioSlack with some rectifier diodes and some 50 and 100 ohm 10w resistors for experimentation.


To answer the question about the initial green 6r resistors value. It was just a guess; I just selected a small available value based on an initial assumption that enough resistance to satisfy the GZ34 was already present in the secondary winding of the PT. Also, I was probably mistaken that since I have a choke, I'd go by the 'choke' recommendations (specifies no resistor). But I am now under the impression the choke does not count because it is not first.