PT question for a 50watt JCM800

[Curranproducer]

SO i am building this 50watt JCM800. I have a 40-18053 PT from classic tone.

according to the 50watt schematic I will need to change the diode rectification from what the 50watter is, to what the spec sheet for the 40-18053 calls for. I am also using 1N5408 diodes on all of my builds. I think they look cool. BUT if you look at the spec sheet it is also showing some 100uf/100uf filtering then sending off the B+ to the rest of the schematic. I have 50uf/50uf 500v F+T caps in this build. My question, do I need to add this extra filtering OR is this just a representation of the 1st filter node point on the 40-18053 spec sheet and stick with what I have for the 50watt schematic? this 40-18053 PT is for a 100watt JCM800. it is showing that the 98v tap goes to the bias section of the amp and on the 50watt schematic the B+ is going right to the bias section along with the choke and other filter node sections. should I empoy this 98v tap OR just roll along with the rest of the schematic for the 50watter? just curious.

[Littlewyan]

Your transformer will work fine both ways I believe, but hook it up the way they have in that schematic so its a full wave rectifier.

With regards to filtering because they used a Full Wave Bridge Rectifier on the 100W amps the filtering was a bit different. One 50uf/50uf cap can will be fine for the mains, just put a jumper across it so the two halves are connected together and you'll have 100uf.

You could use the bias tap. As its there you may as well. I used a bias tap in my Trainwreck Express and all I changed was the first resistor (R30 220K) to something like 470R. You may have to use 1K, not sure. My bias tap was only 70VAC and your's is 98VAC.

Also as you're using a 100W PT it will have a higher current rating so you may find this amp is louder than a normal 50W JCM800. In fact you may end up with a 500VDC B+.

[martin manning]

The 100W PT you have will result in too much voltage. You have to wire it as a FWB (as shown in the spec sheet), and you will get >500VDC, too much for your 500V caps. I strongly recommend getting a 50W PT and wiring it like the JCM800 schematic. If it were me, I'd get a MC 40-18095, which has several options for the HT voltage

[gldtp99]

I've found this Edcor to be an excellent PT for 2204 type builds that will benefit from a non-stock, higher capacity power supply----- it is rated for 250 mA vs the stock 150 mA---- B+ will be @420-425V.
You can use the same rectifier and bias circuits as in the 2204 schematic.
Save the 100 watt Marshall PT for a 100 watt build, for reasons listed in previous posts.

Edcor PT: https://www.edcorusa.com/xpwr037

Or just get a stock Classictone 50 watt Marshall PT if a stock power supply is what you want to build.................. gldtp99

[rogb]

The 100W PT you have will result in too much voltage. You have to wire it as a FWB (as shown in the spec sheet), and you will get >500VDC, too much for your 500V caps. I strongly recommend getting a 50W PT and wiring it like the JCM800 schematic. If it were me, I'd get a MC 40-18095, which has several options for the HT voltage

Yup I used 18095 and 18025 PT for my 50w, both fine and dandy!
5H 120mA choke too.