Curious_George

If you built the original version from 1949 or early 50's I do believe the stories of potential instability on some builds. In addition, depending on the output transformers used, the cap & resistor across the first stage anode resistor and the feedback cap & resistor, there was not much room for error. Layout and parts placement should be well thought out. The Talbot Wright article helps a bit too. IMO, a robust low impedance power supply will help eliminate a lot of the issues. I really like the Edcor output transformers, especially the 25 watt, 7.6k multi-tap version. I believe this is the closet thing you will get to an original Stancor A-8072. The Edcor is a bit smaller, but it also is using M6, which IMO is a better core material.

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The "just in time" inventory concept worked surprisingly well when the supply chain was reliable and consistent. Nothing in the world today is reliable or consistent. Depending on the manufacturer, some were quicker to respond than others to change their strategy. JIT is slowly waning for other inventory strategies that work in our new world order. The challenge now is to stock the "right" inventory versus carrying "a lot of inventory". The right inventory is the stuff you know will sell even if you have 6 months of it.

Depending on my mood, I run my 1974 LaScala's on a 3.5 watt/ch 2A3 amp or a Phase Linear 700B which is really not a 700B anymore since I redesigned the entire driver board section and converted it to full complementary output. In my opinion, 3.5 watts is the minimum I would want for headroom reasons. 1.5/1.75 watts just doesn't leave much room for dynamics even with efficient speakers like Klipsch heritage series.

Have you narrowed down what triode you would like to use? 45 / 2A3 / 300B? I would suggest a new build if you want SET. You can build it yourself or have someone build it for you. You are definitely going to have to do a lot of research, then make a decision. That's the hard part for a first tube amp. Subsequent amps are a little easier each time.

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Of the 2A3's out there barring USA NOS types, I have found the Sovtek 2A3 to be a great value. I have tested them against NOS RCA and I personally don't hear much of a difference, if any, in a blind test. I'm sure that will start a firestorm, but I'm just throwing my opinion out there. For a little over $100USD, the Sovtek 2A3's sound great and are very reliable. I know you said you were looking for 45's, but if your going to build an amp, using 2A3's over 45's won't affect the cost of the amp too much and you'll have twice the power.

Here is my modified Type E network...

Opps, posted to wrong topic.

First, I'd like to applaud Claude (no pun intended there) for his work on the ported Heresy mod. Back in 2012 I asked about a ported Heresy but did not get very far at the time with the project. Life and you know, life has a habit of getting in the way. Now, I have a bit more time on my hands and can tinker more (hopefully). My ported Heresy (circa 1979 version) is using a Celestion TF1225 woofer. The factory specs on the TF1225 are almost identical to the Eminence Delta Pro12A. Measured specs (with a DATS V2) are similar to factory specs, but more favorable for the small Heresy enclosure. I tuned the Heresy enclosure to 55Hz with 4" PVC, 3 5/8" long. Speaker modeling with WinISD shows that F3 is 56.4Hz. That corresponds with a box volume of 1.715 cubic feet. I have also modified my Type E crossover to ALK Universal Type for the Heresy. Stock K77 & K55V are still being used. No room measurements yet, but the TF1225 sounds as good or better than the K22 woofer. Even though the F3 is 56.4 Hz, room gain is making it sound like there is a bit more down below. Similar to the ported LaScala mod (which I have also done), the ported Heresy can benefit from a high-pass active filter with low damping (or a high Q, depends on how you want to look at it). The high-pass filter (below) provides an approximate 18dB/octave roll-off and 5.3dB of boost @ 40Hz. The steep roll-off prevents infra-sonic frequencies from unloading the woofer at high power levels. This was initially designed for the ported LaScala, but works equally well on the ported Heresy. The high-pass filter extends the ported Heresy to an F3 of 44.5Hz. You can definitely hear the extra 10Hz extension.

This woofer is not suitable for a direct replacement in a Heresy. I am not certain what "economical" choices there are out there. I certain that particular topic has come up a good many times. Use the search function and see what comes up. I am fairly new here myself. CG

I tried the MCM woofers listed earlier in this post ans was not happy with the results. I recently came across a woofer that appears to be a great candidate for a "Ported" Heresy project, the Celestion TF1225. They are only $56.99 from J&R Music World. http://celestion.com/product/102/tf1225/ I am currently testing a 3.5 cubic ft ported enclosure with TF1225 woofer, K55V mid / 700 horn and K77 Alnico tweeter. I am also using a Heresy Type E crossover slightly modified for said driver combination. I'll post frequency response graph, impedance graph and cross over schematics soon. So far it sounds great, just like a Heresy, but with more Bass. Preliminary testing shows the response down to about 45Hz (F3) in this enclosure.

I am using a 2A3 SE amp (3.5 Watts per channel) I built from scratch with Heresy's (Circa 1979) and a solid state pre-amp using only the "loudness" function to give me a little bump in the Bass region. I am extremely happy with the way it sounds. The amp is very quiet even though I am using AC on the 2A3 output tubes. If you place your ear right up to the woofer, you can just barely hear 60Hz hum. The mid and tweeter are also very quiet and you can only hear residual noise if your ear is placed right up to those drivers.

MCM 55-2952 Real T/S Parameters measured via Klippel Electrical Parameters #1 Re 8.26 Ohm electrical voice coil resistance at DC Le 0.623 mH frequency independent part of voice coil inductance L2 0.860 mH para-inductance of voice coil R2 9.38 Ohm electrical resistance due to eddy current losses Cmes 981.24 µF electrical capacitance representing moving mass Lces 15.24 mH electrical inductance representing driver compliance Res 18.62 Ohm resistance due to mechanical losses fs 41.2 Hz driver resonance frequency Mechanical Parameters (using laser) Mms 58.935 g mechanical mass of driver diaphragm assembly including air load and voice coil Mmd (Sd) 51.689 g mechanical mass of voice coil and diaphragm without air load Rms 3.225 kg/s mechanical resistance of total-driver losses Cms 0.254 mm/N mechanical compliance of driver suspension Kms 3.94 N/mm mechanical stiffness of driver suspension Bl 7.75 N/A force factor (Bl product) Lambda s 0.059 suspension creep factor Loss factors Qtp 1.453 total Q-factor considering all losses Qms 4.726 mechanical Q-factor of driver in free air considering Rms only Qes 2.097 electrical Q-factor of driver in free air considering Re only Qts 1.452 total Q-factor considering Re and Rms only Vas 107.6013 l equivalent air volume of suspension n0 0.344 % reference efficiency (2 pi-radiation using Re) Lm 87.56 dB characteristic sound pressure level (SPL at 1m for 1W @ Re) Lnom Zn missing dB nominal sensitivity (SPL at 1m for 1W @ Zn) rmse Z 2.30 % root-mean-square fitting error of driver impedance Z(f) rmse Hx 1.75 % root-mean-square fitting error of transfer function Hx (f) Series resistor 0.00 Ohm resistance of series resistor Sd 547.39 cm² diaphragm area Electrical Parameters #2 Re 8.14 Ohm electrical voice coil resistance at DC Le 0.592 mH frequency independent part of voice coil inductance L2 0.966 mH para-inductance of voice coil R2 10.07 Ohm electrical resistance due to eddy current losses Cmes 701.90 µF electrical capacitance representing moving mass Lces 19.51 mH electrical inductance representing driver compliance Res 24.45 Ohm resistance due to mechanical losses fs 43.0 Hz driver resonance frequency Mechanical Parameters (using laser) Mms 58.453 g mechanical mass of driver diaphragm assembly including air load and voice coil Mmd (Sd) 51.207 g mechanical mass of voice coil and diaphragm without air load Rms 3.407 kg/s mechanical resistance of total-driver losses Cms 0.234 mm/N mechanical compliance of driver suspension Kms 4.27 N/mm mechanical stiffness of driver suspension Bl 9.13 N/A force factor (Bl product) Lambda s 0.045 suspension creep factor Loss factors Qtp 1.159 total Q-factor considering all losses Qms 4.637 mechanical Q-factor of driver in free air considering Rms only Qes 1.543 electrical Q-factor of driver in free air considering Re only Qts 1.158 total Q-factor considering Re and Rms only Vas 99.3444 l equivalent air volume of suspension n0 0.492 % reference efficiency (2 pi-radiation using Re) Lm 89.12 dB characteristic sound pressure level (SPL at 1m for 1W @ Re) Lnom 89.05 dB nominal sensitivity (SPL at 1m for 1W @ Zn) rmse Z 2.09 % root-mean-square fitting error of driver impedance Z(f) rmse Hx 1.89 % root-mean-square fitting error of transfer function Hx (f) Series resistor 0.00 Ohm resistance of series resistor Sd 547.39 cm² diaphragm area In addition, the voice coil assembly appears to be out of the magnetic gap. Like they used the wrong "jig" when assembling the woofer. This may account for the low BL product since the VC is barely in the magnetic gap. If the manufacturing quality was better, this woofer might perform quite well in small(er) enclosure.

%*%^@#$ and I just ordered some a few days ago at the "normal" price. MCM = Stupid Head. (Sheldon from Big Bang Theory)

Discussing caps is about as bad as engine oil (Dino vs Synthetic), but I'll jump in anyway... Regarding cap composition, I agree, the composition of the cap is more important than brand. If the "old" oil caps show no sign of leakage and still measure good what makes them "old and tired"? I have used small oil caps similar to the type in the Klipsch crossovers in tube amps I've built in the past. The esoteric oil caps are stupid money and I am not sure I can hear the difference. A good film/foil cap is hard to beat, such as the Bennic brand, and they are inexpensive

So our data (and thinking) yield similar results. My plan is to build some Heresy "clones" for home theater. I wanted the main speakers to go down to at least 50Hz so my sub could take over from there. I prefer the sound of paper cones, even for bass. And the treated cloth accordion surrounds seem to last forever. I have the space for larger enclosures, but try and balance performance vs size.

Well plugging in the "advertised" specs yields an F3 of 50Hz, tuned to 45Hz in a 2 cubic foot box, which is roughly the volume of a Heresy. If the average original Heresy has a roll off of 60~65Hz, then extending that down to 50Hz (for $25) might be worth something. In addition, room gain will net you a few extra dB of bottom end, depending on your speaker placement. When I get my woofer samples, I'll run them on the Klippel and confirm the T/S parameters. Of course there is nothing like building sample enclosures and hearing the results.

Hello All, New to the forum, but not audio. I've recently procured some 1979 Heresy's from the original owner. I've been itching to build something lately and I don't want to cut or hack on the Heresy's. Reading through the posts about ported Heresy's, I found an MCM woofer that appears to have the correct specs to work well in 2 cubic foot ported enclosure (http://www.mcmelectronics.com/product/MCM-AUDIO-SELECT-55-2952-/55-2952). Anybody tried this or have any comments? I figure you could make a new back panel with a port and easily convert from sealed to vented without compromising the original speaker too much, plus you could easily "restore" it for resale value if you wanted.