Supro S6920 Schematic wanted

[Sean Weatherford]

Does anyone know where I might find a schematic for the late '67 blue face Thunder Bolt? I am trying to determine how different this amp is from the earlier S6420 Thunderbolt. I have schematics for both the solid state and tube rectified S6420 thunderbolt. (I am in fact the author of the most readable copies you see floating about.)

I have googled, binged and altavista-ed. No Joy. I am trying to compare the circuits of the later three knob S6920 Thunderbolt with the earlier two knob S6420. I am pretty sure the S6920 is very close to the Harmony 525 (Which is also similar to the Harmony 420.) I have never ran across a S6920 T-bolt in person.

I have a small webpage where I have gathered info about the S6420. I would like to add some info about the S6920 if anyone knows anything.
The Supro S6420 Thunderbolt

Please comment on the content of the page if anything is wrong.

Sean

[tubeswell]

Hi Sean

Thanks for the website of yours on the S6420, and thanks for those schematics. I don't have any info on the S6920 sorry, but I do have a question about the Weber 15F150. I bought one a little while back intending to use it in a S6420 clone, but the one I got was the 30W version. Do you think it'd be alright to put with a S6420? (or should I spring for the 50W version?). TIA Pete

[Sean Weatherford]

Hi Sean

Thanks for the website of yours on the S6420, and thanks for those schematics. I don't have any info on the S6920 sorry, but I do have a question about the Weber 15F150. I bought one a little while back intending to use it in a S6420 clone, but the one I got was the 30W version. Do you think it'd be alright to put with a S6420? (or should I spring for the 50W version?). TIA Pete

I think it will be ok. The cathode biased 6L6's are only pushing about 30 - 35 watts. Unless you run the amp flat out all the time you should be ok. The amp does sound better when pushed. Drop a line to TA over at Weber's Forum to confirm. You will get more speaker breakup with this speaker than you would with a higher wattage unit. Another thing to consider is that the Thunderbolt does not clip the signal into a chain of squarewaves even when pushed. That makes life easier for the speaker.

Sean

[Sean Weatherford]

After more consideration. I think the 15F150 may be borderline. In my own amp, I would risk it. I not sure if can tell you to do the same. One thing you can do is to solder a 220 Ohm 5 or seven watt resistor across the speaker. (Inside the chassis on the wire going to the speaker is best.) This will protect the OT in the event the speaker blows or if the output jack fails or becomes unplugged.

Sean