Metropoulos Forum

Billy Batz wrote:You answered your own question. The 2 bias caps are 8 or 10u. Whichever you can get. I cant be sure which resister your refering to. The one thats attached to the PT is usually 27k in 100W amps and 220k in 50W amps. The rsistor betweent he 2 caps is always 15k and the resistor paralleled to the second cap sets the bias level so its different for every set of tubes. With a bias pot instaleld and for EL34s its usually a 47k resistor.

I've circled the resistor (?) in question.

lol. Thats the bias pot.

Billy Batz wrote:lol. Thats the bias pot.

... buries head in sand with feelings of great stupidity...

I guess its not the best representation of a pot.

No, most people would probably have figured that out. I take things pretty literally, and I've still got a lot ot learn, so we'll chalk this up to my own ignorance.

Thank you for humoring my question with an answer. I've seen other boards not be as patient.

Hi All:

We have passed 2000 downloads from my download page, 2027 to be excact.

There must really be a lot of people who just read, and never post on this Forum. Or every member, even the inactive ones, on these boards have been back 3 times.

Keep ´em coming Billy. There´s a obviously a need for yor fine work.

I know I've been back three times download all the good stuff on it...

I think I got just about everything needed here. I could do a JTM45 but I dont think thats needed. The instructions are very clear.

Hey Dan, great job on the layouts. Just wondering, did you leave out the switching circuit on the 2550 intentionally? I noticed there was no relay or the two push-pull pots.

Yes. First off I didnt decide to do a 2550 layout for the 2 members here, past and present, who actually may build one. I drew a layout up for someone by request and thought Id just make a quick graphic. They requested to leave out the rhythm clip switchmajjigy since it apparently sounds really bad, and they decided not to have it switching. It could easily be added. But thats what I did and I figured why not share it? I did try to make everything fit on a standard 12.5x3.25 board. anything more would have to be off that board or split between 2 boards. That would be easily done.. Theres space inside the 1987 type chassis if you use an X mount tranny.

I'm not sure if there are mistakes here, but the attached schematic identifies the differences between the US 6550 MV amps and the EL34 amps.
1. Splitter for 6550 tubes is 150K or 100K, as apposed to 220K.
2. Bias resistor for 6550 tubes is 47K, as opposed to 56K. In BillyBatz layout, it shows 47K.
3. PT resistor before diode for 6550 tubes is 15K as opposed to 27K.

I'd also like to know if a 25K bias is still OK for a 6550 amp, or would a 10K be a better option? Also, do 6550 tubes require different values for screed grid or swamp resistors?

Ill put it on my to do list to label alternate '6550' values on the 2203 layout.

First of off, excellent pics. They are very easy to follow and much appreciated. I've just got a couple question that I hope you can answer. I'm using the'69 1959 layout and there are a couple differences from the diagrams on the CD that come with the 100watt kit that I purchased from George. There is an extra red wire coming from the filter cap in the upper left corner of the pic connecting to a point on the board with a jumper to the pin next to it. Is there a reason for this as I don't see it connecting to anything else. The other question is with the point where the HT fuse, OT and choke connect. On every layout that I can find the choke wire at this point is colored black, But I thought the black wire from the choke connected to the point next to the purple wire coming from pin 3 of the presence pot and the red wire from the choke would connect to the point with the white OT wire and HT fuse. Hoping you can clear this up for me.



Again, thanks for you time and these excellent layouts.

swissross wrote:First of off, excellent pics. They are very easy to follow and much appreciated.

Thanks.

I've just got a couple question that I hope you can answer. I'm using the'69 1959 layout and there are a couple differences from the diagrams on the CD that come with the 100watt kit that I purchased from George. There is an extra red wire coming from the filter cap in the upper left corner of the pic connecting to a point on the board with a jumper to the pin next to it. Is there a reason for this as I don't see it connecting to anything else.

You'll notice if you look at a few different layouts and schematics and different gut shots of marshalls, some boards have 2 large caps at the power end of the board. They are there to hum from the power supply. Not all amps have them and not all amps need them. Those empty turrets with the jumpers, they are for the .22 caps should you choose to use them. If I had the board tyhat made room for them Id probably just use them. But for the sake of clarity I left them out. The caps connect to either end of the HV wind, then they connect together ont he other end and connect to the junction of the caps in the first filter section along with the CT.

The other question is with the point where the HT fuse, OT and choke connect. On every layout that I can find the choke wire at this point is colored black, But I thought the black wire from the choke connected to the point next to the purple wire coming from pin 3 of the presence pot and the red wire from the choke would connect to the point with the white OT wire and HT fuse. Hoping you can clear this up for me.

Chokes dont have an orientation. In fact not all chokes are color coded. Mine have 2 black leads. Some have a black and red or red and white. If it makes you feel better use the color that is in other layouts for the specific connection but it doesnt matter.

Thanks for the quick reply. All understood now.