Fender 5B3 ?

[macdillard]

I am in the process of building a 5B3 and have a couple of questions that maybe some could help me with...This started out to be a Rickenbacker M11 but when I started comparing the schematics they are pretty much the same. Being there was a layout for the Fender I am building it..I had a chance to measure the Voltages in the Rick and they are somewhat lower that those shown for the Fender. ie; B+ in the Rick measured 323 VDC, Fender shows 350 VDC, the plate voltages for the pre amp tube measured 66 VDC, Fender shows 92 VDC..Question is would you expect there to be much difference in the amps? Other questions is that the Fender layout shows a 100pf cap across the plates of the PI tube. It is not shown on the schematic..What is the purpose of this cap?

Thanks

[Wombaticus]

I am in the process of building a 5B3 and have a couple of questions that maybe some could help me with...This started out to be a Rickenbacker M11 but when I started comparing the schematics they are pretty much the same. Being there was a layout for the Fender I am building it..I had a chance to measure the Voltages in the Rick and they are somewhat lower that those shown for the Fender. ie; B+ in the Rick measured 323 VDC, Fender shows 350 VDC, the plate voltages for the pre amp tube measured 66 VDC, Fender shows 92 VDC..Question is would you expect there to be much difference in the amps? Other questions is that the Fender layout shows a 100pf cap across the plates of the PI tube. It is not shown on the schematic..What is the purpose of this cap?

Thanks

I'd go with the Fender specs, as you can then use a PT intended for a 5E3 (which are widely available, make sure to get one that puts out reasonable voltages with modern 120V mains). Also, the cathode biased 6V6s sound great at those voltages. Use a NOS 5Y3GT to keep the voltages in line along with JJ or NOS 6V6s, which are tough as nails, 'cause it's gonna run really hot with the 250R cathode resistor. The PI cap is presumably to combat HF oscillation arising from poor lead dress, you can probably just leave it out if you do a clean job.
Other than that, er, why a 5B3? The grid leak bias method used for the input valve basically sucks... it's way too dependent on the individual valve characteristics, and Fender abandoned it for a good reason. Also on the down side, the preamp tubes I don't believe are in current production.The paraphrase phase inverter might be interesting to implement though, just to see what one sounds like -- but again, there's a reason Fender moved away from them... I guess I can see building one just as a historical curiosity, but I'm just wondering about your motivation. That said, if you do build it I'd *love* to hear clips.

[macdillard]

Like I said it started out to be a Rick M11. Have a friend to came into procession of the Rick and he just loves the amp. He asked me to see if I could build one that would come close to the Rick. There in the 5B3.The 6SC7's were not hard to come by. I bought them off of e-bay. I just like building amps. Got 5E3, 5F2, three different Marshall 18 Watts, and 5 from the AX84 site. Just a hobby for me..And I can't play guitar..Give them all to my Son.

I am just about finished with this amp. Will finish the wiring and soldering today. The cab is built but not covered yet.(trying to justifying using the original tweed tolex, but it is really pricey). This has been a fun little project. I designed the cab such that I can change out the 5B3, convert it to a 5E3 ( which I know I like) and install it into the existing cab.

[Wombaticus]

Like I said it started out to be a Rick M11. Have a friend to came into procession of the Rick and he just loves the amp. He asked me to see if I could build one that would come close to the Rick. There in the 5B3.The 6SC7's were not hard to come by. I bought them off of e-bay. I just like building amps. Got 5E3, 5F2, three different Marshall 18 Watts, and 5 from the AX84 site. Just a hobby for me..And I can't play guitar..Give them all to my Son.

I am just about finished with this amp. Will finish the wiring and soldering today. The cab is built but not covered yet.(trying to justifying using the original tweed tolex, but it is really pricey). This has been a fun little project. I designed the cab such that I can change out the 5B3, convert it to a 5E3 ( which I know I like) and install it into the existing cab.

Cool. I got curious and did a bit more digging about the 6SC7. Turns out that it is pretty much electrically identical with the 6SL7 (which is still current production), except for a different pinout, and has a shared cathode. The other tidbit is that Bruce from Mission amps has reported that a very high percentage of 6SC7 tubes he encounters turn out to be microphonic. So if this is a problem for you, you can always rewire the socket, bridge the cathode pins, and use 6SL7s, which don't suffer from the microphonics issue.

[macdillard]

Thanks for the info...When I get this finished I will see if I can post a sound clip. I can get my friend to play it and he has recording equipment...Never have tried to post a sound clip so will probably have to get someone to show me how.

[pdf64]

Re paraphase converters, I don't think it would be justified to rule them out just because Fender moved on to different types.
They have a large potential signal level, and the self balancing types are - well - balanced!
Vox actually moved from LTP types in the AC30 and 1st generation (very short lived) AC50 to self balancing paraphase for later AC50s.
Like a cathodyne, you can also get more gain per 12AX7 than with an LTP.

[gsr]

Re paraphase converters, I don't think it would be justified to rule them out just because Fender moved on to different types.
They have a large potential signal level, and the self balancing types are - well - balanced!
Vox actually moved from LTP types in the AC30 and 1st generation (very short lived) AC50 to self balancing paraphase for later AC50s.
Like a cathodyne, you can also get more gain per 12AX7 than with an LTP.

+1 on the paraphase. Just built a 5D3 (with all octal tubes- 6sl7 v1, 6sn7 p.i.). It sounds very warm and creamy with more head room than my 5E3 build.

[macdillard]

Up date on the 5B3 for those that are interested..It is built as a combo using Warehouse Guitar speakers 12" Reaper for the speaker..I did make a few mods to the original build...I up the second power supply 10K resistor to 22K. I upgraded the heater wiring to two leads with a CT and dc elevated by connecting the ct to pin 8 of the 6V6's. This gives me about 19 VDC elevation. I installed a power on/off switch and did away with the switch on the tone control. (the switch on the tone control pot was giving me some hum.). The grounding scheme is buss grounding with the ground point being right at the input jacks. No hum in this amp. I used Magnetic Components Inc transformers for both the pt and the ot. The Ot is their standard for a 5E3 and listed for 20 watts. The PT is a 40-18027, wired 315V-0-315V. It is rated for 100ma which is plenty for this amp. Using this PT allowed me to play with the B+ voltage by changing between a NOS 5Y3 rectifier and a Sovtek 5Y3. The NOS rectifier gave me a B+ of 315 volts with a cathode voltage of 17 volts for the 6V6. The Sovtek gave me a B+ of 340 volts and a cathode voltage of 19 volts. This amp sounds really good. Using the NOS rectifier with the lower B+ the bass notes were just a little bit muddy ( can you describe a note as being muddy?). Going to the higher voltage with the Sovtek rectifier cleaned all of this up. I took the amp to my friend who has the Rick M11 that he likes so much and let him play it. He hooked it up and plugged in a 72 Fender Tellie that he was working on. He really gave it a work out..When he got through he looked at me and said "This is the best sounding amp I have ever played" I asked, do you think it is better that the Rick? he said yes it is. The amp was sitting right beside a 5E3 so we got to kinda of A/B the two.He like the 5B3 best. Now I understand that different players like different sounds,(My guitar playing Son is partial to Gibson guitars and Marshall amps) But this is a really good sounding amp. Friend still has the amp. He asked to keep it over the weekend..I don't have the equipment or the know how to post a sound clip. sorry. wish I could. One thing though, Wombaticus is correct about the availability of the 6SC7's. They will probably get hard to source..The change to the current production 6SL7 is very simple and that is what I will plan on..If you want to see a cool Music shop then go take a look at my friends shop at Mainstreet Musician Supply Small town America is not dead. We are just more than 20 miles off of the interstate so most never get to visit..And Bruce, if you read this, or anyone else, Have any of you done business with Vacuum Tube Supplies (VTS) there in Denver?

[overtone]

I really wish you the best of luck in getting the amp back from your friend!

Thanks for the update because it is always good to read a conclusion to the discussion and work in a thread. This particular one has really informed my next build, a 5B3 or 5C3, for an old 50's Gibson ES with p90s, so thanks again for posting.

[Bruce / Mission Amps]

No, sorry... I have not done any biz with VTS. To be honest, I don't recognize the name.
I looked them up and they about 9 blocks away from the metal polishing shop I use to deburr and polish my steel chassis' before chrome plating so, I'll stop by someday soon.
The Mag Comp Champ PT, 40-18027, is a little light weight for this project but should still work well... the trick would be to continue using the SOVTEK with this amp as the B+ needs to be around 350vdc. The same PT OT combo sounds great if the NOS 5Y3GT is used with fixed bias power tubes.
The 6SC7GT tubes sound great but are getting harder to find.
The 6SL7GTs are so easy to find, I'd rewire the socket to accept them....