Three Amplifiers vs One Man. My DIY quest

[Bogner]

I Like Where This Is Going!

 

[Simon Says]

I have officially started building my project.

I just spent enough money on parts to buy a second-hand AC30CC, so I'm really hoping it will sound great.

In the last couple of weeks, I have mainly focused on reviewing and modifying my plans. I will stick to the magic numbers for the most part, but I have made some modifications to the power supply and grounding scheme. I have moved a few parts around, such as the filtering capacitors closer to the stages they are supposed to filter.

I have also added rectifier tube protection diodes and moved the Pilot Light indicator from the heater supply to the mains primaries.

The most significant modification has been made to the heater supply. In the 60s AC30, one side of the heater was grounded (bolted to the grounding tag on the Normal/Brilliance input tube socket bolt). No one does that anymore, and even back then, it was uncommon. I have disconnected this point and was going back and forth on how to approach it. The DC supply is no-go. I just don't have enough current to do that with 6 ECC tubes. At first, I considered doing the Humdinger (balance the two sides of heater supply to the center tap with a 500R trimmer), but eventually, I settled on the Elevated Heaters. It happens it's really easy with the cathode-biased amps. All I had to do is to connect the heater center tab to the PA tubes cathode. Done. No additional parts. Shout out to pdf64 and 2L man from TGP (and other forums) for guiding me here.

So, the first part of the build I did today was to prepare the tag boards. The 1965 AC30 Top Boost has two rows of 42 tags on each side, and the ones I could buy are the 18-row ones. I went to Worcester (shout-out to the sauce!) to see a friend from work who has a proper man shed. I have cut and joined them to what you can see below.

Now, before I drill the chassis to mount them, I will wait for all the parts I have ordered to do the test fit first. More progress soon.

So far, it's fun!

 

[bodia]

Hell yeah!

 

[Maxime Bousquet]

Stimulating project!!

 

[Simon Says]

Hell yeah!

Stimulating project!!

Thanks.

I have made some visual progress.

My Mouser Electronics order for most passive components has arrived, except for the power supply can caps. I am waiting for shorter tagboard stand-offs before I start putting the board together, as I'm worried about running out of space around the control panel. The parcel from Mojotone with potentiometers, pilot lamp and other hardware is expected to arrive later today, so I can confirm the spacing.

However, I am still waiting for my order from Modulus for all the can capacitors, valve sockets, and other hardware. It's crazy that Modulus is a domestic supplier, yet they are taking longer than US-based retailers.

So far, I have only mounted a couple of resistors for the PSU and bias circuit and a couple of tag-strips to hold the components, wiring for the power stage grid/screen 25W resistors and the rectifier valve. The rectifier valve socket will be replaced with a ceramic base, and I will overspec the PSU and PA a little as this part of the amp will get very hot.

Although I was considering doubling the value for the PA grid resistors and 10x for the screens, I have decided to go with metal film 2W stock values and see what happens. I will be using Vishay PR2 series 2W resistors, flameproof. I want to build the stock circuit first and eventually start modifications later. The golden era AC30's had 0.5w Carbon Composition resistors for the grids and screens. One thing one should know about the AC30 is that with the 50R/250uF bias resistor/capacitor, the EL84 cook on 110%, and with stock screens, the new production EL84 just don't last very long.

Yet, fairly early in my planning, I have decided to use N.O.S EL83 (no typo). Years ago, on now no longer existent Plexi Palace forum, I saw and saved pictures of Rory Gallagher AC30's, which had been modified to accept both the EL84 and EL83's (6P15). It's an easy mod, requiring to link the valve base pin 1 and pin 9 where the 100R screen resistor goes. The EL83 are still easy to obtain and cost just a fraction of NOS EL84's. Sonically, they are similar, yet break up a bit sooner, so I will get the PA crunch sooner than the phase inverter drive. With the link, I will be able to use the EL84 with no issues too.

Anyway, I'll make more progress tomorrow, and mega progress the week commencing May 13th when I will have a whole week to play with electronics and the Modulus order completed.

 

[WingerRules]

I was going to ask if you intended to use EL84m (already answered) as they are more robust with standard AC30 specs, and what transformers you’re going to use.

Looks like you have a plan already for tubes/ tube life. What about the transformers?

 

[Simon Says]

I was going to ask if you intended to use El84m (already answered) as they are more robust with standard AC30 specs, and what transformers you’re going to use.

Looks like you have a plan already for tubes/ tube life. What about the transformers?

Hey Howie, opting for the EL83 has its benefits. If I need to replace them more often, it won't be as heartbreaking. Even with NOS tubes or EL84M's, the stock bias, grids, and screen resistors tend to wear out quickly. By linking pins 1 and 9, I can still use EL84's and maybe keep a special set for unique occasions (a PRS meet-up, anyone?). Regarding transformers, I have decided on domestic Trans-Amp for mains and Pacific Audio for OT and Choke. Shipping Pacific Audio from the States will be a hassle, but I'm ready to handle it. It's interesting to note that this project has cost me more than a second-hand VOX AC30CC, and I haven't even purchased speakers, transformers, or the cab yet.

The Mojotone order has arrived and my amp is beginning to take shape!

 

[Maxime Bousquet]

Thanks.

I have made some visual progress.

My Mouser Electronics order for most passive components has arrived, except for the power supply can caps. I am waiting for shorter tagboard stand-offs before I start putting the board together, as I'm worried about running out of space around the control panel. The parcel from Mojotone with potentiometers, pilot lamp and other hardware is expected to arrive later today, so I can confirm the spacing.

However, I am still waiting for my order from Modulus for all the can capacitors, valve sockets, and other hardware. It's crazy that Modulus is a domestic supplier, yet they are taking longer than US-based retailers.

So far, I have only mounted a couple of resistors for the PSU and bias circuit and a couple of tag-strips to hold the components, wiring for the power stage grid/screen 25W resistors and the rectifier valve. The rectifier valve socket will be replaced with a ceramic base, and I will overspec the PSU and PA a little as this part of the amp will get very hot.

Although I was considering doubling the value for the PA grid resistors and 10x for the screens, I have decided to go with metal film 2W stock values and see what happens. I will be using Vishay PR2 series 2W resistors, flameproof. I want to build the stock circuit first and eventually start modifications later. The golden era AC30's had 0.5w Carbon Composition resistors for the grids and screens. One thing one should know about the AC30 is that with the 50R/250uF bias resistor/capacitor, the EL84 cook on 110%, and with stock screens, the new production EL84 just don't last very long.

Yet, fairly early in my planning, I have decided to use N.O.S EL83 (no typo). Years ago, on now no longer existent Plexi Palace forum, I saw and saved pictures of Rory Gallagher AC30's, which had been modified to accept both the EL84 and EL83's (6P15). It's an easy mod, requiring to link the valve base pin 1 and pin 9 where the 100R screen resistor goes. The EL83 are still easy to obtain and cost just a fraction of NOS EL84's. Sonically, they are similar, yet break up a bit sooner, so I will get the PA crunch sooner than the phase inverter drive. With the link, I will be able to use the EL84 with no issues too.

Anyway, I'll make more progress tomorrow, and mega progress the week commencing May 13th when I will have a whole week to play with electronics and the Modulus order completed.

Thank you so much for sharing!
it's very interesting to see the stages and I'm spectators until the end!

 

[Simon Says]

Thank you so much for sharing!
it's very interesting to see the stages and I'm spectators until the end!

Tomorrow, I will begin assembling the preamp boards and going through the part selection process. I am hopeful that the amplifier will sound as amazing as the components look. Thank you for your kind words, Maxime. Fun fact; out of the 80 (!) resistors in this amplifier, only three carbon composition resistors will be used.

 

[WingerRules]

Hey Howie, opting for the EL83 has its benefits. If I need to replace them more often, it won't be as heartbreaking. Even with NOS tubes or EL84M's, the stock bias, grids, and screen resistors tend to wear out quickly. By linking pins 1 and 9, I can still use EL84's and maybe keep a special set for unique occasions (a PRS meet-up, anyone?). Regarding transformers, I have decided on domestic Trans-Amp for mains and Pacific Audio for OT and Choke. Shipping Pacific Audio from the States will be a hassle, but I'm ready to handle it. It's interesting to note that this project has cost me more than a second-hand VOX AC30CC, and I haven't even purchased speakers, transformers, or the cab yet.

The Mojotone order has arrived and my amp is beginning to take shape!

Looking good so far!

 

[Maxime Bousquet]

Tomorrow, I will begin assembling the preamp boards and going through the part selection process. I am hopeful that the amplifier will sound as amazing as the components look. Thank you for your kind words, Maxime. Fun fact; out of the 80 (!) resistors in this amplifier, only three carbon composition resistors will be used.

Of course How could it be otherwise!
It will be incredible!
You are methodical and choose that high quality parts, you need the know-how but for that I am not worried!

 

[Bogner]

I Want One.

 

[Simon Says]

Of course How could it be otherwise!
It will be incredible!
You are methodical and choose that high quality parts, you need the know-how but for that I am not worried!

There was no math behind it on my side. I'm building this amp, but I'm hardly an amp builder.

I had no much choice as far as Polyester capacitors go. I considered using Sozo capacitors, but they were rated for only 400v and were too large to fit in the amplifier. Also, Sozo did not have some values that were required for the AC30, such as 150nF in the phase inverter. Moreover, the cost of £6 per capacitor was too high, and I needed 27 of them. So, I chose the Vishay MKT1813 line instead. Vishay is known for producing high-quality and reliable passive components, just like PRS is known for guitars. Although they cost £1.50 per piece, they are worth it and then some. They are 630v rated, come in all the required values, have a good track record in AC30 builds. For resistors, I chose Vishay CCF60, which are 1% tolerance metal films, 1w, and are sized like the old 0.5w CC. I was going to use the PR2 line initially, which are 2W metal films, but 5% tolerance. I was going for a similar look to the old Piher's used in British 60's amps. However, I decided to use them only for the PSU and PA because of their wattage rating and kept the CCF60 for most of the preamp for quality reasons. The CCF60 resistors have been used in Soldano's, and Mesa/Boogie still uses them to this day. I used Carbon Composition resistors for the Phase Inverter plates and the tail, which were only three resistors. I chose Ohmite Little Demons for these. The reason for using fewer CC resistors is that they are noisy, whereas Metal Film resistors have 1/10th of the noise level of CC resistors, are closer in tolerance, and do not age quickly. I have spent a considerable amount of time relocating PSU capacitors closer to the stages they are supposed to filter. Additionally, I have worked on moving all the noise-generating factors from the heater supply and spent several hours creating a new grounding scheme. It would be a waste of all this effort if I were to use CC for all preamp positions. The MF's are better components overall. However, I think using CC resistors in strategic places can have certain benefits. You can read more about it at http://www.geofex.com/article_folders/carbon_comp/carboncomp.htm.

For other parts, I went with Cornell Dubilier Silver Mica's for all small value capacitors, and Vishay TE series for cathode bypass electrolytics. The PSU filter caps are spread evenly between German F&T and Kamet/Rifa PEG124.

I Want One.

Dude, you have more amps than Mark Tremonti, save some amps for the rest of us

 

[WingerRules]

I get it on the sozo’s. There are a few places you could put them that are probably worth it, but not the whole amp. And, that’s a good parts list you have there anyway. Those Vishay’s are good. CD mica’s are good, etc. All good stuff! Should be a great amp.

 

[Alnus Rubra]

I Want three.

No surprise there

 

[Simon Says]

I get it on the sozo’s. There are a few places you could put them that are probably worth it, but not the whole amp. And, that’s a good parts list you have there anyway. Those Vishay’s are good. CD mica’s are good, etc. All good stuff! Should be a great amp.

The Sozo's will have their chance. I still have two more amplifiers to build on my bucket list, where the size or voltage won't be as important.

Here are some pictures of the parts I am going to use, which were described above

Cornell Dubilier Silver Mica


Vishay MKT1813


Vishay PR02 2W/5%


Vishay CCF60 1W/1%


Kemet/Rifa PEG124


Vishay TE series


Sprague 30D for cathode bias


I had planned to build the preamp today, but I encountered several issues. The chassis I purchased is a close replica of the mid-60s integrated Top Boost AC30. However, some hole locations, sizes, and spacing are not suitable for the parts available today. For example, the fuse holder went through the panel, so I need to find a bigger one. In a worst-case scenario, I will use some washers. The mains capacitor clamp was also misaligned with the holes drilled in the chassis, but I drilled new ones and it worked fine. Another issue is that the valve sockets' holes were specified as 22mm, not the more common 19mm, leaving me with few choices for the valve bases. I was only able to find 22mm valve bases from Modulus, which luckily are ceramic, a must-have for the AC30. However, the orientation of the valve bases in relation to the predrilled chassis holes is 90 degrees off from the parts layout, making the heater wiring complicated. I am not entirely sure how to approach this yet, but I will take a few days to think about it. Especially, since I have another issue to worry about in the preamp section of the chassis

Woodworking has a general rule - measure twice, cut once. This rule is even more important when building amplifiers. Unfortunately, I made a mistake and now I'm having issues with the placement of stand-offs for the preamp boards. The chassis has already been drilled with the spacing for the long 42 one piece board, but that board doesn't exist. Instead, I had to cut, sand and join several 18 tag long boards to make my own. The lower tag holes has been drilled a bit too low, and the mounting bolts are preventing me from joining the PA/PSU part of the chassis with the L-shaped preamp side of the chassis. I could measure things a few more times, relocate the board 3-5mm up and drill new holes, but I'm annoyed because my chassis will end up looking like a Swiss cheese

Simon not happy!

PA/PSU assembly as it is in its present state, with the surprised Modulus order coming today. I expect to make more progress in two weeks after resolving the issues I discussed and having a house for myself.

 

[Bogner]

No surprise there

I See What You Did There.

 

[Maxime Bousquet]

There was no math behind it on my side. I'm building this amp, but I'm hardly an amp builder.

I had no much choice as far as Polyester capacitors go. I considered using Sozo capacitors, but they were rated for only 400v and were too large to fit in the amplifier. Also, Sozo did not have some values that were required for the AC30, such as 150nF in the phase inverter. Moreover, the cost of £6 per capacitor was too high, and I needed 27 of them. So, I chose the Vishay MKT1813 line instead. Vishay is known for producing high-quality and reliable passive components, just like PRS is known for guitars. Although they cost £1.50 per piece, they are worth it and then some. They are 630v rated, come in all the required values, have a good track record in AC30 builds. For resistors, I chose Vishay CCF60, which are 1% tolerance metal films, 1w, and are sized like the old 0.5w CC. I was going to use the PR2 line initially, which are 2W metal films, but 5% tolerance. I was going for a similar look to the old Piher's used in British 60's amps. However, I decided to use them only for the PSU and PA because of their wattage rating and kept the CCF60 for most of the preamp for quality reasons. The CCF60 resistors have been used in Soldano's, and Mesa/Boogie still uses them to this day. I used Carbon Composition resistors for the Phase Inverter plates and the tail, which were only three resistors. I chose Ohmite Little Demons for these. The reason for using fewer CC resistors is that they are noisy, whereas Metal Film resistors have 1/10th of the noise level of CC resistors, are closer in tolerance, and do not age quickly. I have spent a considerable amount of time relocating PSU capacitors closer to the stages they are supposed to filter. Additionally, I have worked on moving all the noise-generating factors from the heater supply and spent several hours creating a new grounding scheme. It would be a waste of all this effort if I were to use CC for all preamp positions. The MF's are better components overall. However, I think using CC resistors in strategic places can have certain benefits. You can read more about it at http://www.geofex.com/article_folders/carbon_comp/carboncomp.htm.

For other parts, I went with Cornell Dubilier Silver Mica's for all small value capacitors, and Vishay TE series for cathode bypass electrolytics. The PSU filter caps are spread evenly between German F&T and Kamet/Rifa PEG124.


Dude, you have more amps than Mark Tremonti, save some amps for the rest of us

Thanks for the article!
Your selection of parts is very good, it reminds me of my years of study in electronics..
I wanted to do this job just to design and repair the tube amps but it was at the time a low paid job lol! and the miniaturization of the components are hard to repair so I did well to have chosen to be an electrician!

however your project makes me want to build a!! You're good, it's normal to have some problems but you'll have it for sure!

 

[Alnus Rubra]

I See What You Did There.

Said with forum brotherly love.

 

[Prina]

Great pics of the build in progress. Love the 25W resistors!