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Old 20th January 2011, 07:58 AM   #811
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I agree about the importance of the output transformer, though in my case I use a Hammond 126C in 1:1. That sounds good, but it needs a tube with lower plate resistance, which is why my preamp uses a 10Y instead of a 26. I have a Lundahl LL1660/5mA but since the 10y sounds so good I'm lazy to build the 26 version! Using the 10Y with the Hammond OPT was a big step up from 26 with cap output.

And of course the filament supply is crucial - especially with filament bias!

Andy
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Old 20th January 2011, 12:20 PM   #812
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Has anyone tried the LL1680,5mA...It's has a impedance of 15K:600 ohms. I've tried brief and like it alot. Should be a good candidate for a 26 line amp.
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Old 20th January 2011, 02:23 PM   #813
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Quote:
Originally Posted by Vinylsavor View Post
Would you seriously say it is worth trying chokes with different core materials before having the best possible ouptut transformer or optimize the caps in the signal path ??

Thomas
No certainly not!! We all know the "weakest link" thing, and I fully trust your engineering capabilities. Reading your blogs it is common sense that rules and that is a very good thing.
What I meant to say is that very often the focus is on components which are part of the amplifier, taking an often mediocre power supply design for granted.
On somewhat bigger scale, in my experience many DIY'ers are so much focused on building the popular 300B SE amp, forgetting that their 90 dB multiway loudspeakers might ask for something different..
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Old 20th January 2011, 03:51 PM   #814
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Hi!

Quote:
Originally Posted by vt4c View Post
Has anyone tried the LL1680,5mA...It's has a impedance of 15K:600 ohms. I've tried brief and like it alot. Should be a good candidate for a 26 line amp.
I tried it and I think the 1660 in 4.5:1 is much better. If you need higher step down ratios of course you can use the 1680, or the 1689



Thomas
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Old 20th January 2011, 03:56 PM   #815
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Hey Pieter,

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Originally Posted by pieter t View Post
On somewhat bigger scale, in my experience many DIY'ers are so much focused on building the popular 300B SE amp, forgetting that their 90 dB multiway loudspeakers might ask for something different..
Yes, we agree on that. I get many inquiries for 300B amps, but they shall be cheap and people are reluctant to move away from their low efficiency speakers.

It's quite pointless to spend the biggest part of the cost on just the tubes and compromise on the rest.

I fully agree with you on the PSU beeing very important. Yet I miss in all those PSU discussions coverage of different rectifier schemes. Also almost never the big advantage of screen windings between primary and secondary is mentioned. I get my power transformers wound with two independent screen windings and I found a big advantage of going to power transformers with grain oriented core material.

Best regards

Thomas
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Old 20th January 2011, 05:01 PM   #816
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You come to the 300b SET by a process of elimination!

1) you don't want push-pull or parallel SE
2) you don't want to build a power supply over about 450v

So the maximum quality and power you get from these choices is the 300b.

I did think about low voltage versions of 845 or 813, like around 450v, but frankly I couldn't see any advantage at that voltage.

And yes - my speakers are around 90db, but I have a smallish room and listen at lower volumes.

Am I missing something here?

Andy
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Old 20th January 2011, 05:15 PM   #817
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Hi Andy,

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Originally Posted by andyjevans View Post
So the maximum quality and power you get from these choices is the 300b.
Why? I don't get your reasoning at all. The 300B is a very expensive choice. And in my opinion if you want 300B sound go for the real thing, original WEs. Although current 300Bs got better, they are not more than surrogates in my opinion, it is like instant coffee compared with italian espresso

So the 300B for me is only an option if the funds are available to bring all parts of the amp on the same level. If the budget is not available I'd go for a different choice. As I wrote on my blog about the 6CB5A amp.

Quite a few people use such an amp now and some of them replaced quite expensive commercial 300B amps with them!

There are so many choices and possibilities.

All I want to say is that in order to get the maximum sonic qualities, it is important to balance each aspect of the amp. The tube is just one part of many.

Of course there might be good reasons for using that tube even if it is as simple as someone just likes the shape, by all means go ahead and use it and also play with rectifiers if it is fun for you, but don't assume that you get the best out of your amp or preamp by just using a particular tube or rectifier.

Best regards

Thomas
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Old 20th January 2011, 07:16 PM   #818
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Hey Thomas!

I'm glad you mentioned the 6CB5A since when I Googled it I came to this interesting site, which I enjoyed reading:

The Audio Eagle - Thomas Mayer Tube Amp Magic

I actually like the Chinese 300b tubes - I bought a few on ebay, waiting for good prices, and I didn't pay much. The trouble with buying on ebay is that the tubes are usually mid way through their lives, and you need to add a zero to the hours the owners "think" they've done. Bit like how much an alcoholic "thinks" he drinks. But yes, Chinese 300b's rock my particular boat. There are cheaper options like the 2E22 and 1624. I have some of those but haven't tried them yet. The 2a3 PP amps I've built did also sound very good indeed. I have plenty of 10Y but I haven't used them in the output of amps because I'd need much more sensitive speakers. I imagine they are flat out wonderful.

Andy
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Old 20th January 2011, 07:50 PM   #819
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Originally Posted by Rod Coleman View Post
Theo, Keeping the Filament trafo away from the signal tubes & wiring definitely makes sense. But, be sure to keep the rectifier and capacitors close to the trafo - don't use long wires for these, or they will 'transmit' to other circuits! For a 1A regulator, the rectifier-cap CURRENT pulses may be 5A, with fast rise time. Using the names in my application note AN-DHT01 for the filament heater, C1-R1/R2-C2 should be in the PSU chassis.

Then, when you mount the filament regulator (near to the tubes), use a 1000uF 16V Panasonic FC or your favourite low impedance elko. Mount this on the regulator PCB, like George has done.

The same approach with the B+ PSU is recommended.

Keep the filament supply wiring away from the B+ wiring, when you connect the PSU chassis to the Signal Chassis.
Hello Rod,

Thank's for the answar and also for supplying such and excellent description in the the pdf file you sent me along with the regulator board.

Regarding the B+ wiring and filament supply wiring. Do I read you correct when you suggest not putting HT and LT in the same umbilical?

Theo
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Old 20th January 2011, 08:11 PM   #820
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Quote:
Originally Posted by Nightpuma View Post
Hello Rod,

Thank's for the answar and also for supplying such and excellent description in the the pdf file you sent me along with the regulator board.

Regarding the B+ wiring and filament supply wiring. Do I read you correct when you suggest not putting HT and LT in the same umbilical?

Theo
I prefer them to be away from each other. Remember B+ noise comes from a low-impedance source. Cables close together, running for 1 metre, will give strong coupling, and the filament (in common-mode) has about the same voltage sensitivity as the grid.

OK, the regulator buffers this noise from the filament, but we should try not make extra work for the regulator to do!

Also, take care that the rectifier pulses from the filament transformer/rect/cap do not couple to the B+.... it may also happen with shared cable assembly.
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