the Poor Man 660 support thread

[emrr]

[quote author="wtmnmf"]Any reason to prefer one of these over another?

http://store.tubedepot.com/5687.html[/quote]
[quote author="[silent:arts]"]where I bought my tubes:

6BC8:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=250120083458
(12 available)

5687
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=370032463151
(8 available)[/quote]
[quote author="MartyMart"]Re: Valves in the UK, watfordvalves.com has the 5687's @ £7 a piece and
I found some 6BC8's on ebay for around £8 each.
[/quote]
[quote author="analag"][quote author="skal1"]Is this 5687wb/Phillips good for poorman?[/quote]

Should be...

analag[/quote]

http://www.tubesandmore.com/
5687 $3.45
6BC8 $3.71

 

[[silent:arts]]

[quote author="fazeka"]I was thinking about the Lorlin rotaries for use in the PM670. I know that they only have 6 positions, would this mean too broad/big a jump between positions?[/quote]
yes
you COULD get out YOUR sweet spot while testing with a 10K dual potentiometer in series with 5K.
but 6 steps are - mhm - very limited

 

[[silent:arts]]

[quote author="emrr"]http://www.tubesandmore.com/
5687 $3.45
6BC8 $3.71[/quote]
:thumb:

 

[emrr]

[quote author="[silent:arts]"][quote author="fazeka"]I was thinking about the Lorlin rotaries for use in the PM670. I know that they only have 6 positions, would this mean too broad/big a jump between positions?[/quote]
yes
you COULD get out YOUR sweet spot while testing with a 10K dual potentiometer in series with 5K.
but 6 steps are - mhm - very limited[/quote]

Fully agreed. A small # of steps will be either very big jumps or very range limited.

 

[MartyMart]

Wow the tubes and more prices are great !!
I just got all the valves for the PM670 and 2LA2 , it was almost £90 !!
( $170 )

MM

 

[ruairioflaherty]

Question for Rowan, Bernd and Volker

Do you have any thoughts you could share on the importance of tube quality for this circuit? I'm a relative beginner at all of this and even though I've been hanging here for 3 years or so I've devoted all of my energy towards trying to understand solid state. Like many I suppose this will be my first tube build.

So do you have any thoughts to share on what we should be looking for in tubes?

-Is it critical that we get a quality tube for any given section?
-Is there any matching required (I remember Rowan saying that the circuit does not thump despite the lack of matched tubes)

Please forgive me if this is basic stuff. I've ordered a selection of tubes from tubesandmore as the prices are so good. They don't give much info on what they are though.

Cheers,
Ruairi

 

[emrr]

Tubesandmore are one of the oldest american NOS tube suppliers. Service has always been good, in my experience.

Rowan may have built in some balancing circuits; we won't know until we see it, or he tells us. He has commented that tube selection was non-critical, I recall.

Not hoping to open Pandora's box here, but the runaway success of this project may prove to be a test of immediate NOS tube supply (400+ channels = 1600+ tubes). We may see prices rise on these types, as this will probably appear to be a huge and unexpected demand to the suppliers. Anyone got a lead on 500 pieces of each at wholesale rates?

 

[ruairioflaherty]

[quote author="emrr"]Tubesandmore are one of the oldest american NOS tube suppliers. Service has always been good, in my experience.

Rowan may have built in some balancing circuits; we won't know until we see it, or he tells us. He has commented that tube selection was non-critical, I recall.

Not hoping to open Pandora's box here, but the runaway success of this project may prove to be a test of immediate NOS tube supply (400+ channels = 1600+ tubes). We may see prices rise on these types, as this will probably appear to be a huge and unexpected demand to the suppliers. Anyone got a lead on 500 pieces of each at wholesale rates?[/quote]

Thanks for your insight Doug and thanks for the link. Rowan has said many times in the past that he likes to design with lesser known and good value tubes, it's ironic that the success of the project may undermine his goal in such a a way. I fear you may be correct in your fears that we will see prices rise as the dealers see orders come thick and fast.

I think your idea of a bulk by is a good one. Though he's not really a tube guy would Steve at Apex Jr. have the contacts etc to organise such a buy? He's a friend of the forum and a good guy in my dealings with him.

Cheers,
Ruairi

 

[Emperor-TK]

I got my tubes from tubesandmore last week. I got GE's (not 5 star) and Sylvanias.

-Chris

 

[emrr]

tubesandmore; I got 6BC8's in Sylvania's, and 5687's in Philips ECG.

Some of their orange drop cap prices are better than Mouser, too.

 

[Emperor-TK]

I forgot to mention the Philips ECG 5687. I got those too. They had two different 5687's listed, so I tried them both since they were so cheep and I figured that I could always use spares. The Philips ECG sells for $3.45. The GE (also marked as JAN) sells for $7.05 each.

 

[kazper]

In regards to the shorting and non shorting switches from page #4 of this thread. Neve EQ's seemed to use 4.7M or 6.8M ohm between switches as a way to eliminate clicks. Would that idea still work in this situation?

Math seems to say so, but I get the hard stuff and fumble sometime on the little.

 

[PimD]

[quote author="kazper"]In regards to the shorting and non shorting switches from page #4 of this thread. Neve EQ's seemed to use 4.7M or 6.8M ohm between switches as a way to eliminate clicks. Would that idea still work in this situation?

Math seems to say so, but I get the hard stuff and fumble sometime on the little.[/quote]

It would be great if that would work.
Than we could use these switches.
http://www.uraltone.com/kauppa/product_info.php?products_id=1077

 

[bernbrue]

[quote author="PimD"][quote author="kazper"]In regards to the shorting and non shorting switches from page #4 of this thread. Neve EQ's seemed to use 4.7M or 6.8M ohm between switches as a way to eliminate clicks. Would that idea still work in this situation?

Math seems to say so, but I get the hard stuff and fumble sometime on the little.[/quote]

It would be great if that would work.
Than we could use these switches.
http://www.uraltone.com/kauppa/product_info.php?products_id=1077[/quote]


These are exactly the same switches I use for my prototype. Haven´t finished soldering the resistors yet, but the quality of these switches is great.
regards
Bernd

 

[mikeyB]

[quote author="bernbrue"][quote author="PimD"][quote author="kazper"]In regards to the shorting and non shorting switches from page #4 of this thread. Neve EQ's seemed to use 4.7M or 6.8M ohm between switches as a way to eliminate clicks. Would that idea still work in this situation?

Math seems to say so, but I get the hard stuff and fumble sometime on the little.[/quote]

It would be great if that would work.
Than we could use these switches.
http://www.uraltone.com/kauppa/product_info.php?products_id=1077[/quote]


These are exactly the same switches I use for my prototype. Haven´t finished soldering the resistors yet, but the quality of these switches is great.
regards
Bernd[/quote]

Yeah - I been thinking of using these - I seem to recall about 2 years ago, one forum member was trying to organize a bulk buy direct from the manufacturer. IIRC price was €3 each for a quantity of 500
:!: :!: :!:
I'll look through my backup computer for the info - cant find it by forum search. I think the problem was bad communication with the company so it never happened - but just maybe someone out there (or in here!) may have dealings with importing from Taiwan :?:

 

[[silent:arts]]

[quote author="kazper"]In regards to the shorting and non shorting switches from page #4 of this thread. Neve EQ's seemed to use 4.7M or 6.8M ohm between switches as a way to eliminate clicks. Would that idea still work in this situation?[/quote]
no, this won't work here.
but I would expect rather mutes than clicks in the PoorMan using non shorting switches. shouldn't be a problem.

 

[skal1]

stupid ? do i need four of each [6bc8 5687} for a stereo poorman ?

 

[[silent:arts]]

yes, 8 tubes for a stereo unit

 

[khstudio]

I have a few questions:

What is the difference between the 600/10K and 10K/600 transformers :?:

Aren't they the same thing... backwards??? :?
------------------------------------

For those of us who are stuck & can't find (or afford) the 2x24 switches - will 2x12 be sufficient? Also, I ask you guys that already built this... Where is the sweet spot (as in the resistance)? This may help us determine how to set up the 2x12 switch.

------------------------------------

Last question:

for those of us who are working in a mixed (impedance) environment... like using modern 10k & vintage 600ohm equipment -

Do you think a 10k:10k will work on the input... like the LA2A MOD :idea: :?:
Is there enough gain or drive on the front end of the PM670 to make up the difference (or loss of level) when using a 10k:10k input TX???

Thanks

 

[emrr]

[quote author="khstudio"]I have a few questions:

What is the difference between the 600/10K and 10K/600 transformers :?:

Aren't they the same thing... backwards??? :?
------------------------------------

For those of us who are stuck & can't find (or afford) the 2x24 switches - will 2x12 be sufficient? Also, I ask you guys that already built this... Where is the sweet spot (as in the resistance)? This may help us determine how to set up the 2x12 switch.

------------------------------------

Last question:

for those of us who are working in a mixed (impedance) environment... like using modern 10k & vintage 600ohm equipment -

Do you think a 10k:10k will work on the input... like the LA2A MOD :idea: :?:
Is there enough gain or drive on the front end of the PM670 to make up the difference (or loss of level) when using a 10k:10k input TX???

Thanks[/quote]

The 'sweet spot' is going to be a matter of people's relative operating levels and level setting habits. No one else will be able to make a clear call on this, other than to suggest a wide range.


I'm going to theorize on two things:

• 
  1) 10K:10K will probably work, but with reduced ability to drive into deep compression. 600:10K shouldn't have any impedance matching issues with this type of design. The parts list seems to suggest 15K per section, which would equal 30K on a 10K secondary, which would mean 1.8K reflected to the primary; shouldn't be an issue for much of anything. The designer and beta testers will know.
  
  2) Think about the switches; my assumption is they are dual stepped attenuators similar to using a dual pot on the secondary of the two 'input' transformers; the audio input and then also the input of the side chain amp. I may be wrong as to exact position. How many dB per step will you need? If you use a 12 position at 2 dB/step you have a range of 0 to -22 dB, etc etc. Is it enough? Do you want or need finer steps? 24 position at 1 or 1.5 dB/step seems reasonable to me. If I'm right about the position, you could do several different things with varying results:
  • 
    A) fewer steps plus a switchable input pad (to make up for lack of more steps) on the primaries, say 10, 15, or 20 db. Could be a 'U' pad on the audio input, and may need to be an 'H' or 'T' on the side chain input.
    
    B) Use newyorkdave's dual switch 600 ohm variable attenuator on the primary sides. Double the knobs, double the work.
    
    C) Use dual pots, like the Gates Sta-level and several other pieces. Not as accurate, but clearly works 'good enough'. Not that you will find a 15K dual audio pot; there's one rub.
  The designer and beta testers will know.