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Old 11th June 2008, 09:00 AM   #101
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Hi,
Here is a few post from the Welborne forum on Audio Asylum that explain it

In Reply to: Alan Kimmel's Choke Loaded Mu-stage Mod. posted by Snoopyma on April 22, 2004 at 18:26:16:

I did this mod based on twystd's post many moons ago. I agree that it is very musical. I find the highs & detail in general to be very natural, not in you face listen to me, "listen to me, listen to me" type detail, but smooth, natural detail that let's one concentrate on specific musical voices or the entire ensemmble at the listeners discretion. Very natural, very coherent. Note: it's a tight fit in the chasis if you also do some of his other mods, 3 chokes and a battery under tyhe hood, but it all sound much better than the stock Ultimate, which starts out pretty darn good.
In Reply to: Alan Kimmel's Choke Loaded Mu-stage Mod. posted by Snoopyma on April 22, 2004 at 18:26:16:

The break-in seems to be very long for this mod, it's really hard for me to tell about the subtle changes in the highs over a long period of time. The break-in seems to be about 200 hours before it is complete, and my sonic memory doesn't go that far back, but there did seem to be an improvement in the highs. Whether or not it equals the highs of the exotica teflons or not is hard to tell. The only thing I can tell you is I really like the way it sounds, just more musical.

twystd

First buy a pair of Lundahl 1668 chokes, I mounted mine on the sides of the wooden basses away from the signal part of the amp for EMI reasons. Then jumper pin 2 and 4 together on the choke (pin one being furthest from the mounting base, pin 4 closest to the mounting base). Remove R4 and replace with the choke, pin 1 on the choke going to the cathode of the 6AC7 and pin 3 going to the plates of the 6SL7. Remove C2 and replace with a jumper. Remove R6 entirely, then replace R7 with a jumper. That's all there is to it. You said you tried other mods, out of curiosity, what were they, and did they work for you?

twystd

Posted by twystd (A ) on February 13, 2004 at 11:25:51

Anybody else try this mod to thier Laurels? It really seems to take quite a while to break in, but seems to be THE BOMB! After having this mod in my system for over a month, it seems to just get better and better. My brother Dan, who is very reserved with his compliments, came over the other day and was very impressed. He hadn't heard the system since I implamented the mod. He actually got up and shaked my hand, and said it was the best he'd ever heard. I asked him, to stop it, that he was scaring me, and what the hell did he do with Dan!?! It's hard to describe all the things this mod does, but appears to improve everything, with the possible exception of very, very high frequency detail. If I'd use the usual "audiophile" terms to describe it, I'd just sound even sillier. Am I just imagining this, has anyone else tried it?

twystd
Posted by Cpwill (A ) on February 20, 2004 at 15:04:42

In Reply to: Allan Kimmels choke loaded Mu stage. posted by twystd on February 13, 2004 at 11:25:51:

I did this mod per your post a few months back. My findings were similar to yours. it's a keeper.
Posted by twystd (A ) on December 31, 2003 at 11:23:11

I finally got around to installing Alan Kimmel's choke loaded mu stage mod on my way modded Ultimate Laurels. I finished one amp and just couldn't wait, and decided to plug it in with the other monoblock un-modded. I noticed that the sound stage had changed with the center being shifted about 1/2 way towards the left channel (where the modded amp was), and that there seemed to be a kind of bloom from the music that was coming out of the left channel. That was promising, so couldn't wait to hear both channels with the change. At first I noticed that the sound stage was different, hard to put a finger on it, but different. There also seemed to be a better separation of instruments, but the highs and lows were rolled off. I knew that it wasn't fair to make any judgments until it had a chance to break in, so put a 15 ohm 25 watt resistor across the amps binding posts, and put the player on repeat. After about 25 hours gave it another listen, definite improvement of instrument separation, and the bass was starting to come in. Another 24 hours, and the bass was really kicking in, very smooth, highs a little better. After 80 hours, where I'm at now, really nice. The sound stage is bigger and more focused, the bass is huge and tight (I use my amps full range). The amps sound more relaxed and better controlled, and in a word more "musical". The highs never did get back to the hyper-detail I had before. I don't know if that comparison of the lost detail in the highs would go for a more stock amp, as I replaced tantalum resistors and an exotica teflon cap with the choke. The amps are also more dynamic, and I noticed I can get another 3db out of the amps when playing Peter Gabriel's "Up" CD before the bass distorts. All in all really pleased with the mod, it really sounds amazing, much more relaxing to listen to, but still very detailed. As a matter of fact, I find that through most of the range (excluding extreme highs) there is more detail. I find myself saying the old cliché "I'm hearing things in my recordings I've never heard before". I'll trade the loss of detail in the highs any day for the other benefits. Not real sure that the apparent loss in highs is a bad thing, as many felt that the system was too detailed in the extreme highs as it was. Thanks to Alan Kimmel for coming up with this and thanks to Ben for telling me about it. Now I'll finally set back and enjoy the music, as for once I'm not contemplating my next mod (on the amps at least)!;> )

twystd
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Old 11th June 2008, 05:52 PM   #102
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James,

Thanks for the help...I think I think you laid out a good plan start with the resistor path then incorporate a choke. You struck the nail right on the head with the figuring out of the resistor values as I have started down that path last night on a different project.

Do you have any good suggestions on where I should look, where I could start or who to ask about converting the earlier design to 7193 > 6v6 > 300B?

I am asking now! Anyway here are my thoughts. Examine the voltage along the circuit for 7193 >7193 >300B. Then remove the second 7193 and insert the 6v6. I am thinking that the voltage from the plate of the 6v6 to the 300B needs to stay within the present parameters. Is this correct? Is there software that I can use to play around w/ resistor values and see where it takes me?

Thanks

erick
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Old 12th June 2008, 03:27 PM   #103
sgerus is offline sgerus  United States
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James,

I came across this post and wanted to be sure you have read it…. This touches on a lot of your topics. SJS SE 300B with Interstage Transformer Mk2
See post 19 and 21… this guy (Kuei Yang Wang, also known as Thorston) knows what he is talking about, and he spells out how he would build a 300B amplifier in post’s 19&21

You can start with the WE91 clone, and have this as an option.

I just got a pair of grid chokes, so this weekend my we91 clone will end up essentially the same circuit as per post 19….. I let you know how it works out.
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Old 15th June 2008, 10:16 AM   #104
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Default 6j5g (7193) > 6v6 > 300b sch

James,

Just to let you know by pure luck alone I stumbled across the above schematic and attached below. I havent had time to review it but since you have foiled my perfectly happy bliss of building a 7193 > 7193 > 300B I felt I could give you something else to think about.

Erick
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File Type: jpg 6j5 to 6v6g to 300b 2.jpg (96.0 KB, 732 views)
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Old 19th June 2008, 03:56 PM   #105
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Lord, take a couple day hiatus and the thread gets lost, this forum moves fast! Anyways I have been gone for a little while because for those that don't know, which is probably quite a few people, here in Iowa we have been having some of the worst flooding since 15 years. My girlfriend has been home for a while because she couldn't go home or back to work in Iowa City because it was more or less underwater. Here in Des Moines it was bad too, but the water has started to go down and now we are cleaning up. Luckily just 5 min. North of Des Moines where I live things have been dry. However for the past week plus the rising flood waters had been my main concern, especially for my girlfriend.

With that out of the way I can get back to life as normal. I would love to hear from you sgerus about how your experiments with a grid choke turn out. This had been on my short list of mods to consider for this style amplifier. I had considered a anode choke as well but I thought I had read somewhere that a choke load doesn't sound the best in this design. Thanks for the link to that post as well, I am pretty sure I have seen it, but I just didn't pay very close attention to it. That is actually one of the designs I had considered before. He has some interesting points and does answer some questions, thanks!

77seriesIII - I had actually found that schematic right before my big water related distraction. I was going to post it but you got to it first. It seems to be pretty much what you a thinking about, no? I am sorry I ruined your bliss, mine was ruined too though when I posted that I was going to build a JE/Walton 300B. I am kind of glad it was ruined though because it opened up my eyes to a world of other designs and more suitable drivers.

All the time off actually gave me a lot of time to think about the designs for the 300B's that I have considered or looked into. I have had a chance to read a lot more about some of the designs and may have last second changed my mind. A have a couple questions about a different design and didn't want to start a new thread, it is still 300B. I like the 91A design, somewhat simple and the original. However after reading a lot more about the design I think I may go with the DRD instead. The people who have described the sound make it sound more along the lines of what I want out of an amplifier. I am wondering though about a couple of things:

1. Can I use the current design off of Electra-Print but switch the ultrapath cap for a smaller oil one instead of the new electrolytic?

2. Does the cathode bypass cap need to be so huge or can I use a smaller value film?

3. Would I hear much difference if I modified the power supply a little bit to use a 5U4G instead of the UF diodes?

I have also considered a somewhat related design using something like a 417A choke loaded and with a grid choke, maybe in the future.

Cheers

James
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Old 6th July 2008, 07:58 PM   #106
JosM is offline JosM  Netherlands
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Default 300B Summer Build Question

Dear James,

Summer has coming and I think it is time to start building your 300B amp. So I am wondering what it will be. I readed most of the text and replies. In the start I also give some advice and schemas, so if you do not know what to built, you can always use my schema. Remember the 300B is a beautiful tube and needs good company, Good luck with building your amp.

Jos
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Old 7th July 2008, 08:40 PM   #107
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I know I feel really bad that I haven't updated for a long time, I honestly haven't had time at all to build! Work takes a lot of my time, then the flooding, and I just got back from vacation with my girlfriend. I have decided though after reading many pages and reviews that I am going to build a DRD. I know it may be a little advanced learning how to adjust it and what not, but all conclusions seem to be that this is one of the best 300B designs around. I know the 91A is the classic, but the musings on the DRD seem like this is what I want out of this amplifier. I have a couple questions on this design I would like answered though before I proceed:

1. Is there anything I have to consider if I want to run this amp with a B+ of 550v a-la Welborn Labs style, or just adjust accordingly? I like running with this lower B+ partly for safety (I know, still 550v) and partly because I can use Solen PPE's in the PSU no problem.

2. What differences if any would I see between using Shotkey diodes, a 5U4G, or a hybrid of both in the power supply circuit?

3. The DRD I have laid out is pretty much the one seen on the Welborn site. I was going to use a 1k Dale or Caddock Mk132 for the grid stopper and the same but 47k for the resistor to ground, good/correct values or should I fiddle with these a bit?

4. The Ultra-Path cap in most of the designs is a oil ASC (80uF ?), has anyone used a Solen or M-Cap film in this position? Could I use a 40uF Oil and a 40uF film together and gain anything?

5. Can I use a 100uF cap as the cathode bypass on the driver tube? The main reason is because I want to use a film cap here too in the future.

Cheers

James
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Old 9th July 2008, 02:51 PM   #108
sgerus is offline sgerus  United States
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James,

I see you have come full circle on what type of amp to build! I do the same thing… spend more time on what to build than the actual building of the amp!
I have not built on of these, but it’s on my list of options for my next amp, so I have studied the info that’s on the web.

For the B+ Voltage, that all depends on what level you input/driver plate is at, and what level you want to run the 300B at.

For example, given
Input/driver plate at 150V
and the 300B at 300V -61V

You need 211V at the cathode of the 300B (150V+61V=211V)
And 511V at the plate of the 300B (211V+300V=511V)

Same deal with 300B at 350V -74V
224V at the cathode and 574V at the plate (300B)

Some recommendations:
1. build it on a bread board first
2. set the 300B for 350V -74V
3. use a tube rectifier with a C-LC-LC power supply ( if you can, plan the psu so that you can get from 440V to about 590V just by changing the value of the first capacitor… use PSU designer)
4. FYI, the DRD type amp should be built as a mono block amp, so that gives you the perfect opportunity to compare the DRD to a “conventional” amp, say a triode strapped d3a/300B

The only downside I see with the DRD type amp is the high B+ as you mentioned, and the fact that the 300B cathode resistor will give off about 3 times more heat than a conventional amp.
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Old 17th July 2008, 04:01 PM   #109
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Thank you very much for the incite and the calculations, it helps. Currently my biggest headache has been designing the PSU section. For now I will start with a fairly simple but well designed C-L-C style PSU. I am leaving room though since after reading a bit of the comments on Welborne's site about the Terraplane a FET regulator may be in my future. Other than that I do have a few questions regarding some of the other aspects.

I was planing on using AC on all the heaters but after reading a bit I am thinking of using DC on the 300B. I was planing on a C-L-C with some 33kuF TS-HA's. Would I really notice a huge difference between AC and DC from those that have tried it. I was also looking at the Terraplane again and saw the use of the common mode choke in the filament supply. If I implemented this would I need anything after the CMC, as cap or anything, the Terraplane simplified schematic shown says no.

My biggest headache though has been the design of the rectifier section. I like tube rectifiers, though I must admit it is mostly for looks. I know and admit that sand can have it's advantages in this particular area. I had also been considering some HEXFRED's or HiPerFRED's (IXYS). I am thinking now though about a couple of diodes and then a tube. What am I gaining or losing with a hybrid design? Also in a hybrid rectifier do I really need FRED's or can I just use something like UF4007's? Lastly I was wanting to use a 5U4G, would a pair of 6AX4's or 6AU4's be a better choice? I just want to make sure my NOS RCA 5U4G's would be OK.

Cheers

James

Edit: would a 6D22S be a better choice? I guess the 6AU and 6AX and 6D22 all have similar peak current. Basically I want an amp that is dynamic and if I have understood things right that is what sand in the PSU is good at. Though if the tubes can take the peak currents wouldn't the hybrid be better because of the slow turn on and and dampening of SS noise?
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Old 17th July 2008, 05:21 PM   #110
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OK I have been sitting here working some things out trying to delay going to the gym and have another real quick question. I have been reading lots of information and have gotten mixed input on this subject...what is the best tube to use as a driver? This is the short list I have come up with:

6AN4
417A/5842
6C45/437A
D3a
12HG7
C3g

I am fully open to any others. I have seen a couple DRD's (maybe just one, I don't know) with D3a's, where can I buy these things besides eBay? Same with the 6C45, it looks like a awesome tube but am having trouble finding them. On the same note if I wanted to upgrade a 6C45 in the future are the 437A's even somewhat easily obtainable?

Cheers

James
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