Raoul Duke wrote: ↑Mon Dec 02, 2024 8:08 pm
Hi All,
Been in “lurking and learning” mode for awhile and recently decided to put together a Tweedle-Dee.
First step was reading the 22 page thread originated by Charlie - which is a gold mine of info; then on to mhartman’s documentation in “Files”. All very informative and interesting! Many thanks to both those guys as well as all the other contributors! Charlie’s practical approach and narrative (to include the pictures) throughout were my guides and I learned quite a bit - so thanks again Charlie!
I didn’t do a build thread because I wanted to take everything I’ve learned from this fine community in the past year and try to apply it without assistance unless ABSOLUTELY necessary. Anytime I got confused or didn’t understand something - I searched this site as well as EL34.com, Aiken’s info pages, and of course Blencowe’s info pages to review and get a handle on what I was doing. I know this amp isn’t terribly complicated compared to my last three (and I probably should have started with this one) but it really connected a lot of the principles I’ve picked-up over the past 12 or so months in a way that was easy for a novice to follow - so thanks to everyone who’s imparted knowledge to me as I've started this hobby.
Here’s the wrap-up for any beginners like me who want to see the “journey”:
- Used the AES stainless chassis. Thought about saving some dough and using an aluminum blank and doing my own cutting - which I WILL do next time. The AES is nice, but IMO was tricky to work with. Drilling holes was very hard - even with the correct type of bits for stainless; and the stainless reacted differently while chassis grounding with my 100w iron. It all worked out fine in the end - it’s just frustrating to me that two things that are relatively simple for me became somewhat complicated due to my choice of material. Looks purty though.
- Was tempted to add some mods, but stuck to the TAG files with three small exceptions: added a filter cap bleeder resistor, back-up diodes to the rectifier socket HV in, and the fourth input. Otherwise built as spec’d (with 10M PI grid leak).
- Used the “TM 6/14” board plan with an added 33k grid stopper for the 4th input. This board didn’t line up with the stock mounting holes in the AES chassis, and you can’t just use one and extend the other due to the layout; both need re-locating. This also caused the OT holes to need to move apx. 1/4” c-to-c because the new board hole location put the screw slightly under the OT. Tried to find different solutions to these two fairly minor issues and this is how I solved them. I’m sure there are other solutions had I realized these things earlier in the process - but “live and learn” I guess.
- Based on a thread highlighted by sluckey, I opted for the Hammond 290BX PT and used a Mojotone LENCO OT to round-up to free shipping on my tweed order, lol.
- Speaker is a lightly used MOD 12-35 I’ve had in a box for about 15 years. Sounds pretty good - might stay.
- Cab looks close to a TD, but I took a half inch off the depth because I had a 1x10 in the garage. I measured everything 17 times just to be sure the speaker and transformers all had some room to breathe and it worked out fine. Did the floating baffle, but didn’t cover it - opting for the grill cloth frame/velcro approach. Front panels are 3/4” thickness vs the thinner Tweed Deluxe type. First time working with tweed and it worked out great. Experimented with Mapei 711 flooring adhesive to stick it and it worked very well (I already had it, it was cheap to begin with, and only needs one coat on the wood and nothing on the fabric to stick). As with most adhesives - the key is letting it dry and using heat to reactivate as/if needed.
-Experimenting with different rectifiers (5Y3 vs 5V4) and currently have a mid 60’s Sylvania 5Y3 in. The 5V4s seem to sound as though they give more headroom, but the lowest I could get with them (with the current 250R cathode resistor) was 15.6w @ 111.4% per tube on a set of matched JJ 6V6S. I tried four 5Y3s and 5V4s each and the one that sounds best right now actually had the lowest voltages and dissipation. Here’s the final voltages as the amp begins to break-in:
B+1: 365
B+2: 330
B+3: 286
B+4: 285
PT Plates: 354
Volts across cathode: 20.7
V1a: 153.1/1.0
V1b: 157.3/1.0
V2a: 239.2/40.5
V2b: 189.2/1.4
I get 13w per tube @ 92.9%
DISCLAIMER: This is my first cathode bias build - so if my math is off, please correct me. Always ready to learn. I’m fairly confident because I used the Rob Robinette bias calculator page - but if I mis-applied any of that data - it’s my inexperience showing.
I have JJ 12AX7 in both pre and PI for now. I’m sure I’ll try some others. Also thinking about trying some TAD 6V6GT-STRs. Got a set in another amp sitting here, and I believe they are a 14w tube as well.
Overall real happy with this amp. Sounds good and I’m proud to say I didn’t have to bug anyone to get it going, lol. Thanks again everyone; on to the next.
Here’s some pics:
