Hell yeah!
Stimulating project!!
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?
Thank you so much for sharing!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.
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.Thank you so much for sharing!
it's very interesting to see the stages and I'm spectators until the end!
Looking good so far!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!
Of course How could it be otherwise!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.
There was no math behind it on my side. I'm building this amp, but I'm hardly an amp builder.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!
Dude, you have more amps than Mark Tremonti, save some amps for the rest of usI Want One.
I Want three.
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.
I See What You Did There.No surprise there
Thanks for the article!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
I See What You Did There.