Blackface Deluxe Reverb power supply question

[Colossal]

In considering the AB763 Blackface Deluxe Reverb schematic, all power supply electrolytics are 16µF. Immediately following the GZ34 rectifier tube, there are two 16µF caps in parallel.

I'm wondering if a) Leo intentionally used 2x16µF in parallel so that the GZ34 "sees" lower capacitance, but the sum of 32µF provides a decent reservoir for the power tubes and/or b) that capacitances larger than 16µF "back in the day" were uncommon and expensive so that it was more economical to parallel caps to get a larger value.

Would there be any tonal difference or reason <i>not</i> to just go with a single 32µF cap in this first position? (Slightly improved smoothing with parallel caps?) The datasheet for a GZ34 states that capacitance should be <60µF so even larger values than what is in the BFDR would not be a problem although it would probably change the feel somewhat.

Thanks in advance.

[tubeswell]

I'm wondering if a) Leo intentionally used 2x16µF in parallel so that the GZ34 "sees" lower capacitance, but the sum of 32µF provides a decent reservoir for the power tubes and/or b) that capacitances larger than 16µF "back in the day" were uncommon and expensive so that it was more economical to parallel caps to get a larger value.

I'll go with 'b)'

Would there be any tonal difference or reason <i>not</i> to just go with a single 32µF cap in this first position? (Slightly improved smoothing with parallel caps?) The datasheet for a GZ34 states that capacitance should be <60µF so even larger values than what is in the BFDR would not be a problem although it would probably change the feel somewhat.

No diff. using a single 32uF cap. 32uF is 32uF.

60uF is the maximum reservoir capacitance for a GZ34. It is not a compulsory quantum, nor is it some kind of target to aim for. The higher the filter capacitance, the more the sound cleans up.

[Colossal]

I'll go with 'b)'

Thanks man. I have a feeling 'b' had a lot to do with it given that the stock value is just 16µF straight across the PS. So you have adequate capacitance and ONE part number to order.

No diff. using a single 32uF cap. 32uF is 32uF.

Yeah, this makes sense and it seems like it would save a bit of board real estate too just going with the single, higher value cap.

Thanks for the reply!

[jjman]

I'm thinking that a 32u-450v cap may have been large enough in 1962 that they would have needed to use a larger doghouse to cover the caps. And/or a 32u-450v cap may have been more expensive than 2 16u caps.

Of course the “one part number” thing is also a valid reason.

[Firestorm]

All that plus the fact that they didn't think they needed more than 16uf of filtering. All the tweed Deluxes from the 5C3 on, and the brown 6G3, and the non-reverb blackface Deluxe had a single 16uF. Apparently, some early Deluxe Reverbs also only had one 16uF. I suppose when they started hearing some funky notes, they decided to double them up. The only other caps in inventory were 20uF (not enough difference) and 70uF (only 350 volt).

[M Fowler]

Dave,

You are going to go with the higher capitance right?

Leo had a hard time sourcing parts and so do I. I have been researching all over the internet and catalogs especially for certain caps, switches and higher watt resistors for various projects, drives me nuts.

That amp of yours will be nice.

Mark

[Colossal]

Dave,

You are going to go with the higher capitance right?

Mark

Hi Mark,

With these BFDR builds, my original thought was to try a D-style precision power supply, each series pair of electrolytic caps preceded by small value film cap to reduce noise. I had planned to bump up the capacitance at each node in the PS from 16µF to about 23.5µF (2x47µF). After having my curiosity piqued I've since revised that idea to just using Solen Fast caps (http://www.tubedepot.com/solen.html) throughout the PS in place of electrolytics and paralleled small value film caps. Solens are those half-stick-of-dynamite sized polypropylene film caps. A number of guys on AX84 have tried this and have reported a significant increase in overall clarity and noise reduction as well as an improvement in the quality of low end frequencies. I thought this would be an interesting experiment and good application as these amps will be used for clean tones exclusively.

The consensus regarding using large film caps in the PS is that you can actually use a bit <i>less</i> capacitance when replacing an electrolytic and get the same feel. So I am now thinking to just keep the capacitance in my builds right around the same values as the original BFDR or even go just a hair lower so as not to stiffen the amp too much or make it too bright. Solen makes a 15µF cap so that is close and they have a 5% tolerance where standard electrolytics are about +/-20% so I should be fine. They are also rated at 630V which is nice, no need to series caps to get a bit more voltage capacity. The downside is that they are quite large so take up a bit of chassis real estate.

I ordered the transformers this week!

[M Fowler]

Dave,

I didn't get in on the transformer buy had to throw a wedding and now looking to help the kids get a cheap fixer up home.

The cap stack at lower value parrallel would work keeping the total capitance within reason. Or D-style cap board as you said. The idea is to get the ripple in that first stage to almost undectable.

I was reading about using the Solen caps a few days ago and like you said had good results but someone on this forum was saying they were unnessary or too stale. Sounds like it would be worth a try to me.

As long as your having fun. In the picture I am the good looking fella on the left in a band I threw together for the event Spanky Bottom

Mark

[Colossal]

Dave,

I didn't get in on the transformer buy had to throw a wedding and now looking to help the kids get a cheap fixer up home.

I figured you were up to your eyeballs in preparations for the day! We made the quota and the group buy will still be open until the end of August so if you can't help yourself (nudge nudge), you still have some time.

I was reading about using the Solen caps a few days ago and like you said had good results but someone on this forum was saying they were unnessary or too stale. Sounds like it would be worth a try to me.

I can see how they might be sterile or a bit too bright if too much capacitance is provided in the wrong application. Film caps are a lot faster in a PS and can give some extra transparency so I think if the circuit is prone to brightness, the cleaner PS may accentuate this possibly to the detriment of the overall tone. I don't want to overdo it but think that if I am careful I can capture some of the advantages such as improved breadth and low end while keeping excessive brightness in check. I spoke to one guy who said film caps PSs sound great in high gain amps. I may give this a shot next as I am considering a Mark IIC+ type build.

As for 'unnecessary', I think it depends on the application. Some of the inherent qualities of the classic amps we love are due to saggy power supplies that were never designed to be run at 11. And changing that changes the overall tonality. I think it's up to the ear of the beholder and beer-holder. If it sounds good, then it is. I'm of the mind to think that if Leo or Jim or Ken or Dumble had used film caps in their power supplies, then it wouldn't be unnecessary FWIW, I'm gonna give those new SoZo blue molded caps a shot in these amps as well.

As long as your having fun. In the picture I am the good looking fella on the left in a band I threw together for the event Spanky Bottom Mark

Haha, nice to put a face to the name! I love the band name! Everyone loves a nice, spanky bottom Although I'm surprised not to see your 80 Express in action

Best,
Dave

[M Fowler]

Dave,

Some of the added good tone of amps is lower voltage from the tube rectifier.

We were so busy I told the band to set up and play. The wedding party will be there when we can. I grabbed my son's 65w drive combo and Boss distortion pedal, two cords and a Fender Lonestar Strat and out the door we all went off to the dance! I had no time or space on that stage to consider my usual rig. I only played 1 1/2 sets and danced the rest.

This band was a combination of all my friends that have played together in various bands so we knew each others songs. Temporary band name.

Mark

[Colossal]

Some of the added good tone of amps is lower voltage from the tube rectifier.

I am sticking with the GZ34 in these builds. I want to keep the same feel of the good 'ol BFDR but accentuate a warm but tight low end and upper sparkle (sans icepick highs). I think it was Billyz or Firestorm that recommended trying a polystyrene cap for the treble and bright caps.

We were so busy I told the band to set up and play. The wedding party will be there when we can. I grabbed my son's 65w drive combo and Boss distortion pedal, two cords and a Fender Lonestar Strat and out the door we all went off to the dance! I had no time or space on that stage to consider my usual rig. I only played 1 1/2 sets and danced the rest. This band was a combination of all my friends that have played together in various bands so we knew each others songs. Temporary band name.

Sounds like a good time! Hopefully you can get some R & R now.