looks simple and cheap enough to try. I'll try to look for some this weekend.
Right- use the 5k, an extra couple watts isn't worth the tradeoff. Smells like a rebuild to me, no reason you can't tread the DIY path given how bad sales value is in DIY. 6SN7 would be a much better choice than 6SL7, or as mentioned, a solid state driver might be a solid option.
Just in case you do decide to do the rebuild you might be interested in this.
Earlier today I was talking to a friend of mine , Kevin at K&K audio. In the conversation he mentioned having to clear some things out of his store room and on the list are two pairs of output transformers for 300Bs, one from MagneQuest and one from ElectraPrint. My guess is you could likely get a good price on a pair.
Earlier today I was talking to a friend of mine , Kevin at K&K audio. In the conversation he mentioned having to clear some things out of his store room and on the list are two pairs of output transformers for 300Bs, one from MagneQuest and one from ElectraPrint. My guess is you could likely get a good price on a pair.
I dont think this is high quality amp, it has to be rebuild with better parts, circuit and quality in crafmanship. Look at old professional amps and how they were constructed.
Most of the stuff shown on the net by DIY is low quality build stuff, but sometimes with very high quality components soldered and build together in an unexperienced manner.
Especially 300B needs some atention on driver and power supply stability with an exceptional good OPT and power trans to sound excellent.
Most of the stuff shown on the net by DIY is low quality build stuff, but sometimes with very high quality components soldered and build together in an unexperienced manner.
Especially 300B needs some atention on driver and power supply stability with an exceptional good OPT and power trans to sound excellent.
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Ok guys, spent the good part of the day figuring out Eagle and measuring the circuit. If there are mistakes, I apologize in advance.
I've tried to be as accurate as possible and replicate the chassis grounds as they are. Any feedback would be appreciated.
I'm not surprised. Try to get your money back, part it out, modify, or resell. That design is hideous. A 6SL7 simply isn't up to driving the CMiller of the 300B. Additionally, there is the problem of grid current. These power triodes will begin pulling grid current even before Vgk actually goes positive. There are a lot of complaints about disappointing 300B designs, and all of the deficiency traces back to inadequate grid drive. I certainly wouldn't use capacitor coupling, and I would include a decent grid driver, a cathode follower (the 6SL7 makes a lousy cathode follower) or preferably, a power MOSFET source follower.
PS. who the hell uses Lundahl PTXs and Hammond OPTs?
That should be the other way 'round.PPS: Just get rid of it. 80uF ( 😱 ) across a hollow state power diode is way, way, way too much. That's a spec bust on Isurge for sure.
PS. who the hell uses Lundahl PTXs and Hammond OPTs?
Hi Miles
What you write is spot on. Surprising that the rectifier has lasted...
If the amp is using LL1648, the numbered connections in the schematic make no sense either.
Ian
What you write is spot on. Surprising that the rectifier has lasted...
If the amp is using LL1648, the numbered connections in the schematic make no sense either.
Ian
Another example of a badly and against specs designed 300B amp.
300B benefits much from a beefy power tube as modest voltage amp and driver in combination with an excellent pentode input tube. 300B is much demanding. The use of high quality power xfmr and low quality outputs and choke is another misconception. Badly design, badly execution leads to the conclusion of selling this amp fast.
300B benefits much from a beefy power tube as modest voltage amp and driver in combination with an excellent pentode input tube. 300B is much demanding. The use of high quality power xfmr and low quality outputs and choke is another misconception. Badly design, badly execution leads to the conclusion of selling this amp fast.
Ok, so just for fun I simulated the power supply in PSU II. The B+ is probably around 300V. The OP should remove one of the 40uF input caps before turning it on again.
Yes, this is what most of us would consider a severe budget build. The component choices are not well matched at all.
Not sure what schmitz77 says against chokes. I like chokes... 🙂 but choke input is the way to go - which is not possible with these compontents. The sound won't be at the same level as with a well designed choke loaded input or miata-type supply.
Driving the 300b with a 6sl7 cathode follower is definitely another weak point. I already made my suggestion to replace it with a MOSFET follower. If the ZVN0545A can't be found, there are alternatives. STF7N60M2 for example...
You could do much to improve things, but this would all require full re-design with new components which would cost money.
Ian
Yes, this is what most of us would consider a severe budget build. The component choices are not well matched at all.
Not sure what schmitz77 says against chokes. I like chokes... 🙂 but choke input is the way to go - which is not possible with these compontents. The sound won't be at the same level as with a well designed choke loaded input or miata-type supply.
Driving the 300b with a 6sl7 cathode follower is definitely another weak point. I already made my suggestion to replace it with a MOSFET follower. If the ZVN0545A can't be found, there are alternatives. STF7N60M2 for example...
You could do much to improve things, but this would all require full re-design with new components which would cost money.
Ian
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Selling the amp was my exact thought at first glance, but the OP seems to be willing to get into the modification path so I guess that there is maybe another option. Sell the expensive 300B tubes only and rebuild the amp with another less demanding and cheaper output tube. This looks to be a standard basic tube design with a 300B shoved in just for the show, so most the components and the chassis could be salvaged for a less ambitious amplifier. The crusty old filter capacitor in the OP picture should be checked and maybe replaced still.
I like chokes too, Chokes from Lundahl are excellent. but using cheap chokes and cheap OPT with excellent Lundahl power trans is a misconception.
As always, parts and circuits has to be choosen with great experience like an excellent dinner chef would choose its ingredients with great care and cook it with a taste for Michelin stars level of dinner. Otherwise it will be better to boil something pre-cooked in hot water and drink a red wine from a Tetra Pack box. You will be stuffed after the dinner, but not more. The same here. You can hear a 300B with it (but a redesign of the power supply IS necessary), but you will never audition the real qualities of this tube.
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