Any idea about what to do with this irons?

[JimmyPage]

Hi!

This is my first post in the forum...! I hope I don't disturb!

Well, recently a friend of mine gave me the Drake PT and OT of a JCM 800 combo (European version, 50 watter coming from a pair of EL34s) of the 80s, and the choke too. I don't have any idea of where they come, but they work!

I'm planning about using them in an amp, but I'm not sure what exactly. The PT is 345-0-345 and 3400 ohms, so I was thinking in a 36watter maybe. It's possible? it's an stupid thing?

By the other hand, I was thinking in a 6v6 amp, because I have a pair of 18 watters with EL84, and a amp slightly different will be more useful. And I'll prefer, by the same reason, SS rectifier.

At last, I'm not sure about if I can use those irons or not, if I can use 6v6 tubes (a pair? quartet?), about the design of the power supply, etc... Any kind of help will be very apreciated!!

Thanks, and please... sorry for my bad english!

[Phil_S]

Your English is clear enough. You do not need to say you are sorry. I am sorry because I really only have one language to use.

What you describe is good for a 36W amp or a JTM45/Bassman type amp. We can't talk about the JTM45/Bassman here I really think the JTM45 should be OK here. It is the same basic design as the 18W TMB, but with EL34/KT66 and a choke. I guess, though, rule are rules.

[zaphod_phil]

I really think the JTM45 should be OK here. It is the same basic design as the 18W TMB, but with EL34/KT66 and a choke. I guess, though, rule are rules.

Sorry, but that's just not true. The PI is different. The biasing is different - fixed vs cathode. Negative feedback and presence, in one and not the other. The Normal channel is completely different. The way the channels are combined. The choke already mentioned. And it goes on. Otherwise, if we follow your line of reasoning then ultimately all tube amps are the "same basic design". In reality, all that an 18W TMB has in common with a JTM45 is one preamp channel - plus the Marshall sound. In any case a 50W EL34 OT isn't going to be ideal to use with KT66s or 6L6s.

recently a friend of mine gave me the Drake PT and OT of a JCM 800 combo (European version, 50 watter coming from a pair of EL34s) of the 80s, and the choke too. I don't have any idea of where they come, but they work! I'm planning about using them in an amp, but I'm not sure what exactly. The PT is 345-0-345 and 3400 ohms, so I was thinking in a 36watter maybe. It's possible? it's an stupid thing? By the other hand, I was thinking in a 6v6 amp, because I have a pair of 18 watters with EL84, and a amp slightly different will be more useful. And I'll prefer, by the same reason, SS rectifier.

Yes, it's a great idea, and you can build a 36Wish amp with what you have. Probably the coolest way would be to use a pair of EL34s in the power stage, rather than EL84s or 6V6s, since the voltage and impedance are intended for EL34s and they have fantastic Marshall tone. However a quad of 6V6s would also work pretty fine. You could use any of the 18W or 36W designs on this site, along with the modified power section.

[guitarmike2107]

I would go with 4 x 6V6's. Actually you could probably set it up to use 4 x 6v6's or 2 x EL34's

just an idea of course...

BTW I am loving 6v6's just now so my opinion is slightly baised.

[JimmyPage]

Thanks for your answers and ideas... I think that I'll build something with 6v6's, I adore the sound of these tubes and actually I don't have any amp with them. If it's possible, will be perfect.

And... do you know if there is a schematic or layout of a power supply (SS rectifier) that I can use with the PT? Because I have skills to build without any problem, but I don't have any theoric knowledge!

[zaphod_phil]

Just use the power supply design from the 36W Lite, but replace the GZ34 tube with a series-pair of UF4007 fast rectifiers on each side of the PT secondary. The 8.2k resistor in the power supply will probably also need to be increased, say to around 15k, to get the PI and preamp voltages in line with what they should be in a 36W or 18W type amp. Once the amp is built then voltages can be tweaked some more. Try to keep B+1 below 450V so the 6V6s don't start to sound shrill. The power amp cathode resistors will need to be increased to around 270 ohms for 6V6s. In the phase invertor, the 820R/56k resistor combination will need changing to 470R/20k.

http://smg.photobucket.com/albums/v173/ ... mblite.jpg

[JimmyPage]

Thanks, zaphod! Your indications are very helpful! I'm gonna take a look if I have the resistors, capacitors, etc in my "building-room" and, first at all, I'll get the voltages and I'll start the experiments Thanks, I'll keep you informated!