Hey Bonnie1 thanks for the support and offer!Hello Murdock,
If we understand the testing details so far,
-Sec. dcr (not able to measure)
-Sec. L (not provided)
The BV511 ratio is 1:30
If you inject -30dbu (.0245vrms) sine wave into primary, you should have approx. -.5 to 0dbu on Sec. (.735vrms)
(Src. 150- 200 ohm / Load 100k)
If your response signal is super week you have a open winding.
If your response signal is -20dbu then you have a V372 (1:10 ratio) used in V76M.
These levels are in ref. to 1k regardless if lamination has lost some permeability.
If you need further assistance and/or these repaired to original specs. It is most efficient to email AMI/TAB directly [email protected]
After consulting my notes over many years of "V76" expiriences I've got some more info.
The original BV511 has a very outstanding (abnormal) ratio of 1:28, obviously designed to find as much as possibele "noise free" gain.
The many delicate secundary sections windings with extremely tin wire unfortunately have also extremely high internal parasitic capacities.
Mesurred with an 200 ohm generator, and tested with a 5M load, 60Hz is down -6dB, 1Khz - 0 dB, 8 Khz - 4 dB, 10 Khz - 6dB and 20 Khz - 10dB.
Lundahl LL1577 1:14, 60Hz - 0.5dB, 1 Khz - 0 dB, 10 Khz - 0.5 dB, 20 Khz -1dB, 50 Khz -4dB
Further more, very IMORTAND, an original Europian V76 230V wire up and 230V supply will supply the tube heaters with 6.83V. For the correct 6.3V the input voltage should only be about 212V.
Finally i higly recommend bypassing the four 2u capacitors in the middle of the primarys. These are installed to avoide eventually asymetrical 48V phantom to pass the pimarys. If these capacitors by accident are charget, a discharge will induct a very high voltages to the fragilde secondaries, proabebly the reason that so many of these BV511 transformers goes dead.
Yes, the four capacitors form a subsonic (rumble) filter below 40Hz with the inductance of the primary winding. The measured values for the BV511 mentioned by Fairman are not realistic from my point of view, the V76 would not reach its target specifications with that.Than you have another Bv511 than me. Because the good one is essentially flat from 15Hz to 50Khz... And that is with a 150 ohm source and 1M load. Pretty good for a transformer with such a high ratio.
48V phantom didn't exist at the time the v76 were manufactured. The four 2uF caps on the primary were installed for a bass cut to conform to the IRT broadcast norm as far as I know.
But thanks for the tip with the lundahl. But I don't have an v76. I just happen to come across these transformers and maybe wanted to build something around it.
Appears the 1970's production dipped transformer bobbin with the coils in wax. I have not seen wax in the earlier units.
Unfortunately, I can't find the build instruction for the BV511, but there is some interesting information in the one for the V72 input transformer (CT72/1)Appears the 1970's production dipped transformer bobbin with the coils in wax. I have not seen wax in the earlier units.
Might you remember any particular type of transformers you were discussing? Oliver used special shellac mixture on many transformer designs, also many of his design's he specifically didn't use shellac.Yes, strange. I remember Oliver telling me that any kind of potting or dipping of the bobbins and coils was/is detrimental.
Is wax more forgiving that shellac?
Yes, that is correct for the time period. The early CTV72/1 and BV511, hot wax was used to bond the individual coils. Bond magnet wire did not exist yet.Unfortunately, I can't find the build instruction for the BV511, but there is some interesting information in the one for the V72 input transformer (CT72/1)
Here it is written that when winding the bobbin the lacquer-insulated CU wire should be pulled through hot and liquid wax.
Ok, this is a different transformer, but the manufacturer, style and time period (1952) are similar.