Stopień końcowy we wzmacniaczach push-pull realizowany jest na dwóch triodach, tetrodach lub pentodach mocy. We wzmacniaczach PP większą sprawnością charakteryzują się lampy wielosiatkowe - tetrody i pentody. Tetrody i pentody można łączyć z transformatorem tak jak triody w sposób "klasyczny" lub w trybie "ultralinear".
    Tryb ultralinear, to taka konstrukcja transformatora wyjściowego, w którym część napięcia anodowego jest pobierana z uzwojenia anodowego i podawana na siatkę ekranującą tetrody lub pentody. Powstające lokalne sprzężenie zwrotne znacznie poprawia liniowość i pasmo przenoszenia oraz poprawia warunki pracy stopnia końcowego, chociaż zmniejsza nieco sprawność układu.
    W trybie "ultralinear" tetrody lub pentody pracują "w połowie" pomiędzy trybem triodowym a tetrodowym czy pentodowym, zachowując część zalet jednego i drugiego układu: dobrą liniowość triody i wyższą sprawność lamp wielosiatkowych. Triody, mimo że oddają małą moc ( sprawność rzędu 20% ) są chętnie stosowane we wzmacniaczach dla zaawansowanych audiofilów i melomanów.
    Tetrodę czy pentodę łatwo przełączyć w triodowy tryb pracy, zwierając siatki ekranujące z anodami przez opornik niewielkiej wartości. Wzmacniacz, oczywiście będzie miał mniejszą moc, lecz zalety wzmacniacza triodowego pozostaną. Realizacja przejścia z pentodowego trybu ultralinear w tryb triodowy sprowadza się zwyczajnie do odłączenia odczepów ultralinear transformatora od siatek ekranujących lamp EL34 i zmostkowanie tych siatek z anodami przez opornik 100 Ohm.

    This document describes the specific instructions and steps associated with re-wiring the output stage of the Dynaco Stereo-70 vacuum tube power amplifier from the original 'ultra-linea' pentode topology to a full triode topology.
    Following the modification, the efficiency of the output stage will decrease and the resultant power output capability of the amplifier will correspondingly decrease from 35 Watts RMS to approximately 16 Watts RMS.
    Nonetheless, many have reported favorable audible improvements compared to the original UL configuration when configured in the triode mode.

Left Channel:
1. Disconnect your Stereo 70 power amplifier from the AC mains and allow the
internal voltages possibly stored in the electrolytic capacitor to discharge over a
20 minute period.
2. Remove the four screws holding the top cover and remove the top cover.
3. Next remove the bottom plate of the amplifier. You will now be exposed to the
bottom (foil) side of the printed circuit board and all of the amplifier's direct
wiring. Orient the amplifier so that the output connections (speaker connections)
are towards bottom and the input connector (RCA input connector) is at the top.
Beginning with the Left Channel:
4. Refer to Figure 1. At pin 4 of V1 disconnect the GREEN Output Transformer
wire. Cleanly cover the exposed end of the wire with high quality electrical
insulating tape or heat shrink tubing. This wire will remain un-terminated
therefore dress appropriately near the chassis corner.
5. Obtain a 100 ohm, 1/2W, Carbon Film resistor (Mouser # 293-100).
6. Refer to figure 1- Connect one lead of the 100 ohm resistor to pin 3 of V1.
Connect the remaining lead of the 100 ohm resistor to pin 4 of V1.
7. At pin 4 of V2 disconnect the GREEN-WHITE Output Transformer wire. Cleanly
cover the exposed end of the wire with high quality electrical insulating tape or
heat shrink tubing. This wire will remain un-terminated therefore dress
appropriately near the chassis corner.
8. Obtain a 100 ohm, 1/2W, Carbon Film resistor (Mouser # 293-100).
9. Refer to figure 1- Connect one lead of the 100 ohm resistor to pin 3 of V2.
Connect the remaining lead of the 100 ohm resistor to pin 4 of V2.

Right Channel:
10. Refer to Figure 1. At pin 4 of V6 disconnect the GREEN Output Transformer
wire. Cleanly cover the exposed end of the wire with high quality electrical
insulating tape or heat shrink tubing. This wire will remain un-terminated
therefore dress appropriately near the chassis corner.
11. Obtain a 100 ohm, 1/2W, Carbon Film resistor (Mouser # 293-100).
12. Refer to figure 1- Connect one lead of the 100 ohm resistor to pin 3 of V6.
Connect the remaining lead of the 100 ohm resistor to pin 4 of V6.
13. At pin 4 of V7 disconnect the GREEN-WHITE Output Transformer wire. Cleanly
cover the exposed end of the wire with high quality electrical insulating tape or
heat shrink tubing. This wire will remain un-terminated therefore dress
appropriately near the chassis corner.
14. Obtain a 100 ohm, 1/2W, Carbon Film resistor (Mouser # 293-100).
15. Refer to figure 1- Connect one lead of the 100 ohm resistor to pin 3 of V7.
Connect the remaining lead of the 100 ohm resistor to pin 4 of V7.
16. Rotate both the Left and Right Bias Adjust potentiometers Fully
Counterclockwise (when viewed from the top of the amplifier).
17. Position the amplifier so that you may safely readjust the operating bias in each
channel. The correct bias voltage as measured on pin #8 of the front panel octal
socket (you may wish to refer to Dynaco Stereo 70 manual for the details) is 1.56 VDC.
18. If it is difficult or impossible to set the amplifier operating bias current you may
wish to execute the Stereo-70 Bias Expansion modification as described at our
website (www.curcioaudio.com).
19. Replace the bottom plate and top cover and secure with the four screws.