3rd Gen started

[Dr d]

Stunning amp you have built here, Ian. The attention to detail is stunning. One thing I have learned recently is that the cap foil orientation on these 2nd and 3rd generation amps was very different to the later amps. The photos that I have studied indicates that the 2nd generation amps all tended to have the cap foils oriented toward the pots. It’s the same with the 3rd generation amps except for the bass cap which is oriented toward the valves. It has been muted that HAD was possibly trying to scoop the mids by doing this. Might be worth a try?

[martin manning]

In the photos, is the orientation indicated by a mark added by the builder, or a factory label, which is likely to be random in orientation?

[dbharris]

In the photos, is the orientation indicated by a mark added by the builder, or a factory label, which is likely to be random in orientation?

I can't see any separate marking in the photos other than how the caps are labeled. I wonder if members here who have been inside 2nd and 3rd Gen amps might chime in and share more info?

For what it's worth, those old Sprague 6ps and Di-film caps tend to be marked correctly. Yes, you will find one every now and then that was printed on the wrong side. But not nearly in the same numbers as say modern production 6ps.

Could that bass cap have been marked wrong and that is why it was installed with the silkscreen that way? It's plausible. Do we know that HAD tested for outside foil on each cap vs trusting the label?

-Dan

[martin manning]

All good questions. Recent production does not even have the outer foil bar on the label.

[Dr d]

In the photos, is the orientation indicated by a mark added by the builder, or a factory label, which is likely to be random in orientation?

Hi Martin, the caps are factory labeled. Modern 6PSs aren't labeled. Here are a couple photos of 3rd gen amps showing a whole board and a close up...#70 and #54 respectively.

[Dr d]

In the photos, is the orientation indicated by a mark added by the builder, or a factory label, which is likely to be random in orientation?

I can't see any separate marking in the photos other than how the caps are labeled. I wonder if members here who have been inside 2nd and 3rd Gen amps might chime in and share more info?

For what it's worth, those old Sprague 6ps and Di-film caps tend to be marked correctly. Yes, you will find one every now and then that was printed on the wrong side. But not nearly in the same numbers as say modern production 6ps.

Could that bass cap have been marked wrong and that is why it was installed with the silkscreen that way? It's plausible. Do we know that HAD tested for outside foil on each cap vs trusting the label?

-Dan

Hi Dan, please see my response to Martin. Both photos from different amps show the foil markings in the same place which, IMO. rules out coincidence.

[dbharris]

In the photos, is the orientation indicated by a mark added by the builder, or a factory label, which is likely to be random in orientation?

I can't see any separate marking in the photos other than how the caps are labeled. I wonder if members here who have been inside 2nd and 3rd Gen amps might chime in and share more info?

For what it's worth, those old Sprague 6ps and Di-film caps tend to be marked correctly. Yes, you will find one every now and then that was printed on the wrong side. But not nearly in the same numbers as say modern production 6ps.

Could that bass cap have been marked wrong and that is why it was installed with the silkscreen that way? It's plausible. Do we know that HAD tested for outside foil on each cap vs trusting the label?

-Dan

Hi Dan, please see my response to Martin. Both photos from different amps show the foil markings in the same place which, IMO. rules out coincidence.

Very interesting! #54 is a 2nd Gen chassis (slide switches) but with the 3rd Gen arrangement on the bass pot and some other interesting unique tweaks to the circuit.

[Dr d]

I can't see any separate marking in the photos other than how the caps are labeled. I wonder if members here who have been inside 2nd and 3rd Gen amps might chime in and share more info?

For what it's worth, those old Sprague 6ps and Di-film caps tend to be marked correctly. Yes, you will find one every now and then that was printed on the wrong side. But not nearly in the same numbers as say modern production 6ps.

Could that bass cap have been marked wrong and that is why it was installed with the silkscreen that way? It's plausible. Do we know that HAD tested for outside foil on each cap vs trusting the label?

-Dan

Hi Dan, please see my response to Martin. Both photos from different amps show the foil markings in the same place which, IMO. rules out coincidence.

Very interesting! #54 is a 2nd Gen chassis (slide switches) but with the 3rd Gen arrangement on the bass pot and some other interesting unique tweaks to the circuit.

Yes, #54 is a really interesting amp. 12AX7 PI etc etc. Found the #54 link on Raoul Dukes "New Build and 102 thoughts" thread. Page 2 i think in discussion section.

[Dr d]

Update: I've swapped out a few resistors for period correct ones and this is really turning out to be one of my favorite amps. I ended up ordering a cab with vox grill and brown suede so I'll post an update when that arrives.

I also changed the PS dropper from a 22K to a 27K after reading a post with B+ voltages from an actual specimen. My V1 B+ was around 288V and the real ODS had around 260V. I found the amp softened a little and fattened up nicely... lots of fun to play.

Something I've been playing around with quite a bit is choke orientation. In chatting with Chris Merren a while back, he mentioned choke orientation. I built myself a small box with a switch to reverse the choke polarity. I had been just tack soldering the choke wires but I found this box way more immediate. After changing resistors in this amp (mostly early 70s 5% pihers) I found the amp became a bit more boomy. Swapped the choke and there was "the sound". The choke orientation makes a big difference (in this amp as well as all my other amps) . I would seriously recommend trying it on an amp you are familiar with.



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Hi Ian, out of curiosity I reversed the choke leads to see what would happen. The amp sounded lifeless after the change with little sustain etc etc. Changed the leads back to the way they were and the amp sounded clearer and the sustain returned. It would seem that by luck I had connected the choke in the optimum way round. I was really taken aback by the effect it had. What a revelation!

[ijedouglas]

Hi Ian, out of curiosity I reversed the choke leads to see what would happen. The amp sounded lifeless after the change with little sustain etc etc. Changed the leads back to the way they were and the amp sounded clearer and the sustain returned. It would seem that by luck I had connected the choke in the optimum way round. I was really taken aback by the effect it had. What a revelation!

Once you hear it you can't unhear it

[jazzbass]

Hi Jan,

demo, demo, demo please...

Franco

[Stephen1966]

Hi Jan,

demo, demo, demo please...

Franco

You have to try it yourself Franco, lossy mp3's are not going to cut the mustard. I had to live with it for a while to properly understand what I was hearing.

The A/B box allows you to hear the difference straightaway, subtle, but noticeable... it takes a matter of time to determine whether you prefer it one way or the other though.

[martin manning]

You have to try it yourself Franco, lossy mp3's are not going to cut the mustard. I had to live with it for a while to properly understand what I was hearing.

The A/B box allows you to hear the difference straightaway, subtle, but noticeable... it takes a matter of time to determine whether you prefer it one way or the other though.

I agree with you on the A/B switch, but this description makes me think that there isn't any significant difference.
Here you can test your ears: https://www.npr.org/sections/therecord/ ... io-quality

[dbharris]

You have to try it yourself Franco, lossy mp3's are not going to cut the mustard. I had to live with it for a while to properly understand what I was hearing.

The A/B box allows you to hear the difference straightaway, subtle, but noticeable... it takes a matter of time to determine whether you prefer it one way or the other though.

I agree with you on the A/B switch, but this description makes me think that there isn't any significant difference.
Here you can test your ears: https://www.npr.org/sections/therecord/ ... io-quality

That is very interesting. I selected uncompressed twice and and the middle option 4 times. Listening with good quality headphones but over Bluetooth. Being a Millennial, I wonder if part of that is an unconscious preference for slightly compressed audio since that is how I would have consumed music in my formative years.

-Dan

[ijedouglas]

You have to try it yourself Franco, lossy mp3's are not going to cut the mustard. I had to live with it for a while to properly understand what I was hearing.

The A/B box allows you to hear the difference straightaway, subtle, but noticeable... it takes a matter of time to determine whether you prefer it one way or the other though.

I agree with you on the A/B switch, but this description makes me think that there isn't any significant difference.
Here you can test your ears: https://www.npr.org/sections/therecord/ ... io-quality

Martin, why don't you try an A/B switch and let us know what you hear? It's certainly not subtle for me. I have also had my wife choose without telling her what I was doing... every time she picked the clearer orientation. It was not subtle for her either.