1. Summary. 1/08/2016 Steanes 976B Amplifier & Speaker Combo Page 1 of 8. Steanes Model 976B & Speaker Combo. Serial No

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1 /08/06 Steanes 96 Amplifier & Speaker Combo Page of 8. Summary Steanes Model 96 & Speaker Combo. Serial No. 66. AX microphone gain stage with volume pot to AX mixer stage, with PU input through volume pot to mixer stage. Output of mixer stage to tone control and then to AX feedback input stage to cathodyne phase splitter. 6M push-pull output stage with common cathode bias. Output transformer secondary with separate feedback winding, and floating 00V distribution. 6V fullwave rectifier with two RC droppers. Excellent condition. Original white plastic Steanes badge on top grill, but 98-9 manufacture date indicates Philips manufacture with Steanes badging. Green thread lock marked fixings. Components Power Transformer.096, x9. 0-CT-0, 6V ~A, 6V?A. Output Transformer TYPE with VSNP stamp. 8kΩ PP (DCR=90Ω); 0-0Ω- 00Ω-000Ω (0-0-00V);.Ω F-F. CAPs Ducon uf 00V Ducon ET Ducon High Seal 8 Pots IRC 86 or 8G curve C Tubes (all Miniwatt) 6V Miniwatt 8K kc 8J (kc=6x, 8=98 or 68) 6M Miniwatt 9A M 8L (M=EL80=6M; 8=98) 6M Miniwatt 8H M 8G (M=EL80=6M; 8G=98??) AX Miniwatt 8I mc6 Δ8G (Philips Herlin 98) AX Miniwatt 8K mc6 Δ8I (Philips Herlin 98) Two open-backed speaker boxes that join back-to-back with clips, such that amplifier and cables fit inside to provide a single unit with one carry handle. Dark green vinyl with red piping on plywood. Each box with Rola M 8 speaker (W, Ω coil, F cone) and Rola (CEL8 8M6) isocore potted speaker transformer (date stamp Mar 96) with kω:ω ratio, with parallel wiring to amplifier (0Ω loading). Vinyl and speaker cloth in very good condition. A few minor hairline tears near rim of cones. Issues: No power switch. Old wax and electrolytic capacitors. Mains wiring close to circuitry. Floating speakers. Spare 6V winding. Not the best grounding. Speakers use line transformers.

2 /08/06 Steanes 96 Amplifier & Speaker Combo Page of 8. Modifications for Guitar Amplifier Main fuse changed to 0.A slow blow. Fuse added to PT secondary CT (0.A Fast IEC x0). N00 added in series with each rectifier plate for 6V. Improved grounding scheme. On switch added to rear panel. Electrolytics and wax coupling caps replaced. PU Volume pot replaced with dual gang and used as post-pi volume. Grid stoppers added. 6M cathode Ω sense resistors added. 6M screen stoppers increased, and extra screen supply filtering.

3 /08/06 Steanes 96 Amplifier & Speaker Combo Page of 8 x 0VDC 90pF MOVs added across each OT half-winding. RC network removed from across PP. OT secondary grounded. Neoprene feet pads. Replace AX stages with AU to reduce gain. Added.6H choke to VS supply. Re-biased input stages for better use of AU. To do: Replace rubber feet. Methyl cellulose based glue, and thin Kozo paper for speaker cone repair. Suspect V valve socket heater sometimes doesn t connect confirm both 6M heaters are on!. Measurements Voltage rail regulation. Modified circuit. Rail 0VAC mains VDC, VACrms Idle condition (AX, no choke) 0VAC mains VDC, VACrms Idle condition (AU changes) VS 00,. (0V turn-on pk) 00,. (0V turn-on pk) VS 88,.6 80, 0. VS 0, 0, VS,, Cathode 9.8 (ma).w 9.8 (ma).w Heater Heater?? Sec HT VA, V, V,.V 0V, 08V,.8V VA 0V,.0V 9V,.V V 60, 9.V 88, 68.V Power transformer primary DC resistance: 0Ω (LU-LK); 6Ω (RD-LK). Power transformer secondary DC resistance: 88Ω. Heater current requirement is: x 0. x (6V) =.6A indicates a 60-CT-60, 6V A, 6V ~0.A. OT with.kω resistive load: Cranked output up to 08VAC (0.6W). Hum negligible. Hiss noticeable but minor.. Design Info

4 /08/06 Steanes 96 Amplifier & Speaker Combo Page of 8. Input stages AX For the first two AX stages have a common kω cathode bias; VA-V; VS = V; Va=; Rk=k; Vk=.V; Ia=0.mA; RLdc=0kΩ. AX K Changing to a AU will draw more current, and raise the cathode bias to? The anode load should be reduced from 0k to about 00k, and the supply dropper reduced from k to k. AU K

5 /08/06 Steanes 96 Amplifier & Speaker Combo Page of 8. Feedback stage AX The feedback AX stage; VA; VS = 0V; Va=; Rk=k; Vk=.0V; Ia=0.mA; RLdc=0kΩ. AX K Changing to a AU will draw more current, and raise the cathode bias to? The anode load should be reduced from 0k to about 00k, and the supply dropper reduced from k to k. AU K

6 /08/06 Steanes 96 Amplifier & Speaker Combo Page 6 of 8. Phase Inverter stage AX in split-load (cathodyne) config VS= 0V. Rk=k. Vgk=.V. Vk=6.V. Va=9V. Vak= 0V. Anode current = (0-9)/00k=0.6mA. AX K Changing to a AU will draw more current, and raise the cathode bias to? The anode/cathode loads should be reduced from 00k to about k, and the supply dropper reduced from k to k AU K

7 /08/06 Steanes 96 Amplifier & Speaker Combo Page of 8. Output Stage Class A push-pull output stage, common cathode bias. The 8KΩ impedance plate-to-plate OPT presents signal currents into each tube with a KΩ impedance with both tubes conducting, to KΩ load impedance at higher levels. No pentode characteristic curves are available for 6M, and similar EL curves are shown but at a lower 0V screen (actual screen is about 80V at idle so bias voltage is close to 0V). As the output loading increases, the supply voltage VS to the output valve plates sags from about 00-0=90V towards 90V. Plate DC voltage will be lower than VS by an amount up to ~8V (ie. plate-cathode sags to about 60V) due to OPT half resistance of about 9Ω with a peak current of up to about 0.A, and cathode bias drop of 8V. Screen voltage will vary from about 80 towards 6V under steady-state heavy load (ie. screen-cathode sags to about 6-8 = V). The maximum output valve bias current allowed is dependant on the maximum recommended plate dissipation assume % of 9W = 6.8W: Ibias(max) = Pd / Vb = 6.8W / 90V = ma, or about ma of cathode current. For a peak plate current of 00mA, then the nominal output power of the amplifier would be: (Ipk) x Rpp / 8 = 0. x 0. x 8k / 8 = 0W. For this maximum signal condition, the rms OPT current draw is likely about 6mA (6% of peak), and the average VS power consumed is about 60V x 0.06Arms =W, and the OPT loss is about (0.06) x 90Ω = 0.8W, so the tube plates dissipate 9.W 0.8W = W, or just under.w each, which is well below max design level.

8 /08/06 Steanes 96 Amplifier & Speaker Combo Page 8 of 8. Power Supplies The 6V is rated to feed 0uF with secondary winding resistance >Ω from 0VAC, and 90mA loading for a 6VDC output, and has a hot switch peak current rating of 900mA, and a continuous peak current rating of 0mA. The effective series resistance is 0Ω x (60/0) 8Ω = 0Ω, which is fine. PSUD indicates a hot switched peak of up to 900mA, and a steady-state continuous of 0mApk at idle, which appears to be fine for cranked output. The steady-state PT secondary CT current at idle is about 0mArms, and rising to 0mArms for a 0ms period for a hot switch event, which would allow a 00mA Fast IEC fuse to be used (min rating of 0ms at.x rating multiplier). 60mAdc, DCR=0Ω (Wurlitzer 0009) choke is added in series with k dropper from VS to VS to reduce screen voltage ripple from.6vrms to 0.Vrms.

9 6 STEANES 96, S.N. 66 Original PU INPUT PU VOLUME VS D VS 00 D 0K M 0N 9 6M V VS VS VS 0K 0K 0K TRANS 90.K P-P, DCR C MIC INPUT 0K AX VA 0N MIC VOLUME V 6 0K 0N N TONE TONE 0NF AX VA V 6 8, uf V 0 VS RD LK 000 RED WH OUTPUT C M K uf V 0K 8 N K, uf M K 0N 0K 0K VS 00 6M V TRANS FEEDACK 80 F F A HEATER- TRANS.096 6V VS VS VS 0VAC MAINS GRN AG VOLTAGE RAILS QTY 60V K K TRANS VALVE 0 LU uf uf uf HEATER RAIL IDLE R 6M 0 RED 9 9 VS 8V 6V A V 00V 00V VS 0V AX 0 DCR 6V 6M 6M AX AX VS 6V 6.V A HEATER- 6.V 60V 0 LK GRN,, 9R GRN Title 6V V Size Number Revision Date: -Jul-06 Sheet of File: C:\Program Files\Design Explorer 99 SE\Examples\Projects\Amplifier Drawn y: Modules.ddb 6 A

10 6 STEANES 96, S.N. 66 Modified VS D VS K D 0N PU VOLUME 6M V C INPUT M 0K VS AU VA MIC VOLUME N 00V M V 8 VS 6 0N N TONE TONE N K VS N AU VA, 00uF 0K M V 6 8 K, 0N VS 0K 0K 00uF V K 0K 80 0K 660V VS 660V 6M V TRANS 90.K P-P, DCR LK 0K RED RD 000 OUTPUT WH C K 00uF V TRANS FEEDACK F F A AG A 0VAC MAINS TRANS.096 GRN 0 LU 60V 0 RED R 0 DCR 0 LK 9R 60V GRN N00 N00 x0 0mA HEATER- 6V 6V V VS K uf 60mA DCR=0 VS uf 00V K VS uf 00V K VOLTAGE RAILS RAIL VS IDLE 00V,.Vrms VS 80V, 0.Vrms VS 0V VS V HEATER- 6.V 6 VS uf 00V TRANS HEATER 6.V A GRN 6V 6M VALVE 6M 6V AU QTY 6M, 9 Title Size AU, 9 Number AU Revision Date: -Aug-06 Sheet of File: C:\Program Files\Design Explorer 99 SE\Examples\Projects\Amplifier Drawn y: Modules.ddb A